Attaching a DSLR to a Swift 380T

[LouiseScot]

This is a follow-up post to my first hack comparing a Chinese DSLR adapter to a cheap 28mm astronomy EP which I posted on Jan 12th. Coincidentally, Oliver has just yesterday uploaded a YouTube video on the subject https://www.youtube.com/watch?v=mTwwJZKEfgo
Anyway, my first go with a cheap 28mm 2" astronomy EP was a bit disappointing because of the large amount of distortion. So I purchased a 25mm 1.25" better quality ('ED') EP which reputedly had low distortion. I've done a comparison between the ED EP, the dslr adapter, and one of the actual Swift EPs. All are easy to fit with a bit of 3D printing to make suitable adapters. When I first purchased the dslr adapter I incorporated a helical focuser in the optical train. This made it easy to make the fine adjustments needed to get the camera sensor parfocal. I've generally been using a Canon 1100d plus a low-profile t-ring. Here are some images of a micrometer slide taken with each method (reduced to about 26% of original). The micrometer slide is useful because it shows up distortion quite well.

1. DSLR adapter

DSLRAdapt_3_26pc.jpg (80.76 KiB) Viewed 9152 times

2. Swift EP

380T_EP_0001_26pc.jpg (75 KiB) Viewed 9152 times

3. 25mm ED

EP_1.25_7mm+5mm_1_26pc.jpg (76.62 KiB) Viewed 9152 times

I think the biggest difference between the various adapters is the field of view. I did a test with the Swift EP without the helical focuser in place and was able to get a bigger fov but at the expense of loss of parfocality. As Oliver mentions in his video, you really want to be close to parfocal with what you see visually. All the adapters have some degrees of distortion but none of them are overly bad. The distortion can be reduced by increasing the distance to the sensor though at the price of a narrower field of view. Also, the wider the fov, the more darkening is apparent at the edges - presumably caused by vignetting. Below are examples of each optic with images of a diatom strew.

Louise

[LouiseScot]

Here are the diatom strew images:

DSLR adapter

DSLRAdapt_Diatoms_1_29pc.jpg (74.92 KiB) Viewed 9149 times

Swift EP

380T_EP_Diatoms_1_29pc.jpg (76.94 KiB) Viewed 9149 times

25mm ED

EP_1.25_7mm+5mm_Diatoms_1_29pc.jpg (63.71 KiB) Viewed 9149 times

Oh, I should have mentioned that all images were at 40x using the Swift objective


Louise

[LouiseScot]

Here are pics of each setup:

DSLR Adapter:

DSLR_Adapter_15pc.jpg (30.08 KiB) Viewed 9138 times

380T EP:

SwiftEP_15pc.jpg (29.3 KiB) Viewed 9138 times

25mm ED:

ED25mm_15pc.jpg (27.79 KiB) Viewed 9138 times

The dslr adapter comes with a standard t-ring. It's used with a 30.5mm collar (supplied with the adapter) in the 1.25" helical focuser. The Swift EP is also used with the same collar plus a 3D printed adapter at the dslr end. The 25mm ED EP
just slots into the helical focuser with another 3D adapter at the dslr end. The Swift comes with an adjustable extension tube for the trinocular port. It's used here in a minimised mode with the end pushed into the helical focuser.
As an afterthought, Oliver's video reminded me that, if using a microscope EP, I should really position it so that it's visually parfocal with the other eyepieces and then connect the camera. That's without the collar and it puts it lower down into the helical focuser. The latter has a brass compression ring to hold it in place (could make another collar). I just used an adapter at the camera end:

EP slightly lower

380T_EPinHelical.jpg (24.47 KiB) Viewed 9138 times

You might think that with the trinocular EP in focus the image would be parfocal with the oculars but it isn't - quite. It might just need some fiddling about with spacing.

Louise

[LouiseScot]

The lower EP with the diatom strew:

380T_EP_inside_Diatoms_29pc.jpg (71.55 KiB) Viewed 9138 times

Louise

[Hobbyst46]

I wonder how the Nikon objectives would perform in the setup. Say, the 28mm EP, which in my opinion produced less distortions than the other two.
How the stage micrometer images would appear.

[LouiseScot]

Hiya

I only have a 20x Nikon CF plan but wanted to stick to the Swift 40x for the comparison, since that's the objective I use most often. I don't think there's a great deal between the different types though I thought the microscope EP was quite good. The 25mm ED EP might have been better if the microscope tube was a larger diameter so would then give less vignetting - but stuck with the design. There is an internal relay lens but I'm not sure exactly what it does but there's no easy way of getting at it or removing it.

Louise

[LouiseScot]

If anyone is interested, here is a link for the helical focuser I used:

https://www.ebay.co.uk/itm/SV108-1-25-D ... Sw-X9dNW5V

And a link for the dslr adapter (though it's shot up in price - it's probably not a good idea to buy some thinks from China at the moment... A shortage of shipping containers, apparently. It will be Chinese New Year too, soon)

https://www.ebay.co.uk/itm/Microscope-A ... 2749.l2649

Louise

[Hobbyst46]

My own equipment is somewhat "analogous" in the following senses:

1. decent but obviously not top optics of the microscope (by today's standard and features)
2. finite tube length, partial correction of aberrations in the objectives.
2. a decent, fairly basic camera with ASP-C sensor, with an old mechanical 50mm prime lens.
3. an improvised mechanical adapter, without lenses.

The illumination is filtered cool white LED and an achromat-aplanat condenser.
There is no separate helical focuser. A regular Zeiss viewing eyepiece in the trino photo tube is exactly parfocal with the viewing bino eyepieces. For afocal photography.
The same trino eyepiece can be raised a few mm above its normal position for focal (AKA direct projection) photography, namely without a camera lens.
Have tried both configurations. The three main issues were chromatic aberrations, pincushion distortion (roughly 10% at periphery) and a hot spot in the center. None of them was totally unacceptable according to my non-photographer judgement.

However:
1) Afocal yielded generally better images than direct projection.
2) Neofluar and Planapo yielded better images than Plan achromats (as perhaps expected). Very little CA, no distortion and a negligible hot spot.

If permitted, I could post a small demo of 40X objectives, neofluar vs plan achro, both under identical afocal condition.

[LouiseScot]

My own equipment is somewhat "analogous" in the following senses:

1. decent but obviously not top optics of the microscope (by today's standard and features)
2. finite tube length, partial correction of aberrations in the objectives.
2. a decent, fairly basic camera with ASP-C sensor, with an old mechanical 50mm prime lens.
3. an improvised mechanical adapter, without lenses.

The illumination is filtered cool white LED and an achromat-aplanat condenser.
There is no separate helical focuser. A regular Zeiss viewing eyepiece in the trino photo tube is exactly parfocal with the viewing bino eyepieces. For afocal photography.
The same trino eyepiece can be raised a few mm above its normal position for focal photography, namely without a camera lens.
Have tried both configurations. The three main issues were chromatic aberrations, pincushion distortion (roughly 10% at periphery) and a hot spot in the center. None of them was totally unacceptable according to my non-photographer judgement.

However:
1) Afocal yielded better images than direct projection.
2) Neofluar and Planapo yielded better images than Plan achromats (as expected). Very little CA, no distortion and a negligible hot spot.

If permitted, I could post a small demo of 40X objectives, neofluar vs plan achro, both under identical afocal condition.

Central hot spots are usually caused by internal reflections. You can reduce or remove them by, where possible, spraying the offending internal surfaces with blackboard paint, or similar very matt black paint. You can get a good idea which surfaces are causing the problem by just eyeballing down the tube using max illumination but without the camera attached, obvs.
I think I'm quite happy with what I have apart from still getting some vignetting. I'm working on a Mk3 version with the ED EP and the narrow trinocular tube removed completely. The trinocular port without the tube is 25mm in diameter. I'm still getting some vignetting. It looks like the only way of dealing with it is to increase the ED EP - sensor distance in order to project a larger light cone - but that results in a narrower field of view.

Louise

[Stomias]

Nice that the helical focuser is 1.25" the standard for telescopic adapters. Over 50 years as an amateur astronomer and I have a box full of 1.25 adapters of every kind.....Unfortunately none of my microscopes have 1.25" anything, I wish they did!

[LouiseScot]

Nice that the helical focuser is 1.25" the standard for telescopic adapters. Over 50 years as an amateur astronomer and I have a box full of 1.25 adapters of every kind.....Unfortunately none of my microscopes have 1.25" anything, I wish they did!

Neither do mine but I just 3D printed the adapters I've used . However, with an APS-C-sized sensor I'm still getting darkening at the edges I used to be able to use my old microscope with direct projection and a dslr with no vignetting and no darkening. It seems to be an inherent problem with the Swift 380T as I can't seem to get around it but I'll keep trying!

Louise

[Naphthalene]

The the black lines on the ruler images of LouiseScot have blurry sides with green/blue contours, like they are illuminated sidewise

Could anyone please tell where do these artifacts come from? I'm using identical DSLR adapter, and I find these effects very annoying.
I would like to know, could such chromatic aberration be introduced by the adapter? Or do they solely derive from using non-apochromat objective?

[Stomias]

Yes chromatic aberration

[Naphthalene]

Thanks, Stomias . But could you specify - does the adapter contribute to it or this aberration is caused only by the objective ?

[LouiseScot]

My own equipment is somewhat "analogous" in the following senses:

1. decent but obviously not top optics of the microscope (by today's standard and features)
2. finite tube length, partial correction of aberrations in the objectives.
2. a decent, fairly basic camera with ASP-C sensor, with an old mechanical 50mm prime lens.
3. an improvised mechanical adapter, without lenses.

The illumination is filtered cool white LED and an achromat-aplanat condenser.
There is no separate helical focuser. A regular Zeiss viewing eyepiece in the trino photo tube is exactly parfocal with the viewing bino eyepieces. For afocal photography.
The same trino eyepiece can be raised a few mm above its normal position for focal (AKA direct projection) photography, namely without a camera lens.
Have tried both configurations. The three main issues were chromatic aberrations, pincushion distortion (roughly 10% at periphery) and a hot spot in the center. None of them was totally unacceptable according to my non-photographer judgement.

However:
1) Afocal yielded generally better images than direct projection.
2) Neofluar and Planapo yielded better images than Plan achromats (as perhaps expected). Very little CA, no distortion and a negligible hot spot.

If permitted, I could post a small demo of 40X objectives, neofluar vs plan achro, both under identical afocal condition.

Hi again - a quick update! I decided to have a go with a camera lens attached but I still need to have another lens in the optical train so I've stuck with the astro ED one for now. It does seem to give a better illuminated field but, so far, at a cost of a smaller fov. I find it a little odd that I can get an image with or without the camera lens being in place _ I'm sure there's a good (optics theory) explanation for that! Anyway, here's a comparison with and without a camera lens (an old basic Canon efs 18-55mm):

With ED EP but no camera lens:

FullT+7+2_29pc_bw.jpg (64.89 KiB) Viewed 8968 times

With ED EP plus the camera lens:

18-55Lens+7+5-3_29pc_bw.jpg (69.14 KiB) Viewed 8968 times

Stage micrometer with ED+camera lens:

18-55Lens_microm2_29pcbw.jpg (69.55 KiB) Viewed 8968 times

I've converted each one to B+W.

I haven't done a test to compare just the ED adjusted to give the same fov as I get with the camera lens but, as things stand, having the camera lens in place does seem better. I set up the camera lens to be parfocal but (again!) it isn't quite, though only a tiny bit out - I can see an almost focused image in the oculars when focused for the camera. I need to shorten the distance ever so slightly between the EP and the trinocular tube port to get it spot on. I can probably do that, and can also probably do without the helical focuser and just have a fixed length tube. I think I'm getting there! Oh, Yes, I'd like to see demos of your lenses - some full frame images would be good

Regards

Louise

[Hobbyst46]

Yes, I have used the Canon kit zoom 15-45mm lens for photomicrography, however I find a fully manual 50mm 1.7 (Minolta MD) prime lens more compact and somewhat better.

Here are the demos. "Focal" means direct projection: without camera lens, with eyepiece raised on a collar.
Afocal - camera lens plus ordinary eyepiece, fully inserted into the photo tube, as for viewing. Near perfect parfocality.
(the notion of exact parfocality along with other useful hints learnt from experts around here).

Photos were post-processed as follows: grayish background was whitened, image was resized and cropped (the two bottom ones - by about 10%).

[LouiseScot]

Yes, I have used the Canon kit zoom 15-45mm lens for photomicrography, however I find a fully manual 50mm 1.7 (Minolta MD) prime lens more compact and somewhat better.

Here are the demos. "Focal" means direct projection: without camera lens, with eyepiece raised on a collar.
Afocal - camera lens plus ordinary eyepiece, fully inserted into the photo tube, as for viewing. Near perfect parfocality.
(the notion of exact parfocality along with other useful hints learnt from experts around here).

Photos were post-processed as follows: grayish background was whitened, image was resized and cropped (the two bottom ones - by about 10%).

Ok, thanks - I'd like to see the uncropped versions, if possible? I can't see much difference between the focal and afocal images apart from fov. Although it's technically a 18-55 zoom that I'm using, it's used at a fixed 55mm (held in place with a custom clip ) and in manual mode, of course. I don't really have any other short camera lenses - just a cheap 75-300mm zoom.

Louise

[Scarodactyl]

I can't see much difference between the focal and afocal images apart from fov.
Louise

There is significant color fringing in the focal image, as well as some distortion of the straight lines.

[LouiseScot]

I can't see much difference between the focal and afocal images apart from fov.
Louise

There is significant color fringing in the focal image, as well as some distortion of the straight lines.

Yes, there is! Though I don't pretend to understand how a camera lens fixes that?

Louise

[viktor j nilsson]

I can't see much difference between the focal and afocal images apart from fov.
Louise

There is significant color fringing in the focal image, as well as some distortion of the straight lines.

Yes, there is! Though I don't pretend to understand how a camera lens fixes that?

Louise

The focal method (raised eyepiece) forces the eyepiece to work outside its design specifications, introducing aberrations. The afocal method (eyepiece fully seated, camera lens focused at infinity) allows the eyepiece and objective to work exactly as designed, minimizing aberrations. At least that's how it works when you are using objectives and eyepieces that were designed to work together.

In your case, however, you are using objectives that likely require some further corrections, and eyepieces that aren't designed to provide these corrections. In that case it's very hard to say what will happen.

[Hobbyst46]

...
Ok, thanks - I'd like to see the uncropped versions, if possible? I can't see much difference between the focal and afocal images apart from fov. Although it's technically a 18-55 zoom that I'm using, it's used at a fixed 55mm (held in place with a custom clip ) and in manual mode, of course. I don't really have any other short camera lenses - just a cheap 75-300mm zoom.

FOV size and vignetting considerations:
AFAIK, for that for the APS-C sensor, if the eyepiece is 10X, the camera lens should have 40mm FL. Mine is a 8X eyepiece, so a 50mm FL camera lens.
With a zoom, I would simply wrap some cellotape around the barrel, to keep the zoom ratio fixed.

Here are uncropped versions of the above images (40X0.75 neofluar vs 40X0.65 plan achro objective).
The afocal vs focal comparison above is not cropped.
I add here another afocal vs focal comparison, this one with a 16X0.4 neofluar Ph2 objective. Uncropped. Essentially the same differences as with the 40X objective.
(P.S. some of theses photos were posted years ago.)

[LouiseScot]

There is significant color fringing in the focal image, as well as some distortion of the straight lines.

Yes, there is! Though I don't pretend to understand how a camera lens fixes that?

Louise

The focal method (raised eyepiece) forces the eyepiece to work outside its design specifications, introducing aberrations. The afocal method (eyepiece fully seated, camera lens focused at infinity) allows the eyepiece and objective to work exactly as designed, minimizing aberrations. At least that's how it works when you are using objectives and eyepieces that were designed to work together.

In your case, however, you are using objectives that likely require some further corrections, and eyepieces that aren't designed to provide these corrections. In that case it's very hard to say what will happen.

Ok - thanks. Bear in mind it is only a Swift380T! The Swift objectives aren't even plan - just plain achros!
Louise

[LouiseScot]

...
Ok, thanks - I'd like to see the uncropped versions, if possible? I can't see much difference between the focal and afocal images apart from fov. Although it's technically a 18-55 zoom that I'm using, it's used at a fixed 55mm (held in place with a custom clip ) and in manual mode, of course. I don't really have any other short camera lenses - just a cheap 75-300mm zoom.

FOV size and vignetting considerations:
AFAIK, for that for the APS-C sensor, if the eyepiece is 10X, the camera lens should have 40mm FL. Mine is a 8X eyepiece, so a 50mm FL camera lens.
With a zoom, I would simply wrap some cellotape around the barrel, to keep the zoom ratio fixed.

Here are uncropped versions of the above images (40X0.75 neofluar vs 40X0.65 plan achro objective).
The afocal vs focal comparison above is not cropped.
I add here another afocal vs focal comparison, this one with a 16X0.4 neofluar Ph2 objective. Uncropped. Essentially the same differences as with the 40X objective.
(P.S. some of theses photos were posted years ago.)

Hi again

As mentioned before, I just made some 3d-printed clips to hold the 'zoom' part of the lens in place. They work fine
I've been experimenting with different camera focal lengths. I think the ED eyepiece is around 11x in microscope terms. The different camera focal lengths affect the fov but the wider the fov, the more distortion is apparent.
Here is a quick comparison of ED eyepiece vs 10x eyepiece at camera lens fl=~45mm and ~38mm:

Afocal

ED EP, fl=45mm:

Afocal_45mmED28pcbw85pc - Copy.jpg (49.92 KiB) Viewed 8848 times

10x EP, fl=45mm:

Afocal_45mm10x28pcbw85pc - Copy.jpg (50.22 KiB) Viewed 8848 times

ED EP, fl=38mm:

Afocal_38mmED228pc_bw85pc.jpg (56.09 KiB) Viewed 8848 times

10x EP, fl=38mm:

Afocal_38mm10x28pcbw85.jpg (69.34 KiB) Viewed 8848 times

Louise

[Hobbyst46]

Ok - thanks. Bear in mind it is only a Swift380T! The Swift objectives aren't even plan - just plain achros!

That is why I asked about similar tests with the Nikon CF objectives.

Yet, on the whole, at least the ED eyepiece with the 40X and camera FL of 38mm yield decent images, suitable for imaging "real life" specimens. Good !

[blekenbleu]

Nice that the helical focuser is 1.25" the standard for telescopic adapters.
Over 50 years as an amateur astronomer and I have a box full of 1.25 adapters of every kind.....
Unfortunately none of my microscopes have 1.25" anything, I wish they did!

Some microscopes have oculars and eye tubes with o.d. 1.25" or slightly less (28-30mm).
Using a strip of e.g. brass shim stock to fill in the difference:


... a T2 to 1.25 adapter with brass compression ring, e.g.:
https://www.amazon.com/gp/product/B082HC7DYY
.. can be repurposed for clamping a camera afocally,
in this case using an M42-T2 male-male coupler and camera lens filter step-down ring:


Full 35mm cameras will want a correspondingly longer lens to avoid vignetting, but 40mm works for APS-C: