Does a DSLR adapter need a lens in it?

[wporter]

Viewing eyepieces will also project a real image, and are not that different from projection eyepieces in that regard. This is easily confirmed by holding a ground glass screen or frosted slide above your normal (viewing) eyepiece; you will get a real image projected upon the screen. The real and virtual images are both in focus (parfocal, so to speak) only at a particular distance of the screen from the eyepiece; but the real image can be refocussed by the focus of the microscope if your screen or image plane of the sensor or film is not at this distance.

Projection eyepieces per se are optimized for projection out to a certain distance to a film plane or sensor, and may have corrections for CA, planarity, and SA for a given film holder. But it is possible to use a normal viewing eyepiece in a phototube and get great results, depending on how the manufacturer designed the eyepieces and camera adapters, etc.

[Scarodactyl]

Oh, fair enough. My understanding was a viewing eyepiece had to be raised some from its normal position to get it to project, but I hadn't had occasion to try it.
Edit: oh I guess I have tried it on my sz7. Wasn't super happy with the results, though, but I guess that varies from system to system.

[MichaelG.]

Hmmm, okay, that's kind of what I suspected. But now I'm confused. Is the Wild 6x eyepiece that apochronaut told me to get a photo/projection eyepiece? It doesn't say it anywhere on the page. Also, the first link (the lot of 4, this one: https://www.ebay.com/itm/LOT-Wild-Heerb ... SwH3ddFOx7 ) has one 6x one that explicitly says "phot" on the eyepiece, making me think that one is a photo eyepiece and the other 6x ones aren't...

Am I missing something?

To a first approximation, the two types are very similar and it’s possible to use many decent visual eyepieces as projective photo eyepieces simply by lifting them about 5mm.

Like racing motorcycles, however ... at the limits of performance, every tiny detail of the design is important.

MichaelG.
.

Edit: My comments are probably superfluous ... the last two posts came in whilst I was drafting.

[apochronaut]

Whether you use a visual eyepiece or a projection eyepiece in your photo system is neither here nor there. They both can do the same thing. Wporter covered why , photo eyepieces are used in a system that has been engineered for them. However, in your case, you don't have a photo eyepiece or tube lens or relay lens, whatever one wants to call it , that has been engineered to optimize photography with your objectives. This means that one has to experiment a little to find one, a tall order, since your objectives are not exactly what one would choose as primary lenses with which to make well corrected, flat, photos.

The idea is to find an eyepiece that will as much as possible compensate for the deficiencies of your objectives. They are not all the same. All projection eyepieces are engineered to specifically do that for a certain group of objectives and they don't necessarily do that for others. All of the "projection" eyepieces at my disposal were variable failures ( about 8 of them). They either cropped the field , poorly corrected for lateral ca and coma with the test objective, or were difficult to get to fill the sensor, while also getting close to being parfocal. Some were designed to flatten the field with a series of objectives and they did not do that well with my test objective.The Wild 6X K H was overall the best in making the best out of a bad situation.

It is important to keep in mind that the three photos are corner to corner, right across a 20mm f.o.v. If you can live wihout that criteria, you probably can find a photo eyepiece that does a good enough job but you will have to test it in order to determine that. Visual determination of the performance of photo eyepieces is very difficult because it is hard to see what amplification of the ca will be like on the sensor.
Plan objectives will make an enormous difference in that.

[iconoclastica]

If your microscopy doesn't need correcting eyepieces then you do not need any lens in your photo pathway. No lens is always better than a cheap lens and possibly cheaper too. All what needs be done is to catch the primary image on your sensor. The primary image is located near the bottom of the eyepiece and at the same distance above the shoulder of your objective in or above the phototube. With a snippet of translucent paper you can easily figure out where it is (150mm on a 160mm finite system). It may be necessary to screw off the phototube - if the primary image falls within the tube you'll need something shorter anyway. On my optiphot I completely removed the tube and replaced it with adapter rings, extension tubes and a helicoid for exact positioning.

The primary image is large enough for an aps-c sensor. I couldn't tell how it works out for FF, but it can be measured on the translucent paper used to find the image. Even if it falls off towards the corners one may wonder if an enlarging lens would be any help, for it won't introduce better resolution, so you might just as well crop the image. This also depends of the quality of the objective and how well you have set up the condenser.

If you system does need correcting eyepieces, your bad luck is that you will need a correcting lens in the photopathway too.

[apochronaut]

With which objectives? Very few microscope objectives provide an image that does not need correcting. There are some well known notable ones and even some of those require field flattening. The camera sensor is unlike an eye/brain complex, in that it must receive a completely flat image corner to corner. A person's brain can compensate somewhat for curvature of field and utilize out of focus portions of the image. We also become accustomed to racking the focus slightly , allowing our brain to fill in the blanks, so to speak. Not so with a camera sensor. You get what you get. Yes, with certain objectives, the image circle is large enough and the image well corrected enough that one could get away with filling a APS-C sensor corner to corner with a pretty good image but in most cases and this one for sure, the bulk of the image being produced by the objectives is malcorrected and in need of as much help as is possible from a relay lens.

[iconoclastica]

Now focus stacking is a standard procedure this is no longer entirely true. I am getting xcellent results with the procedure as described.

[apochronaut]

Focus stacking does not control lateral c.a. or coma, both serious issues with many low grade non plan objectives. The original poster was not asking about focus stacking, though. Perhaps you can assist the o.p'er with some information tabout how he can obtain corner to corner planarity and colour correction with his objectives across the entire microscope field using focus stacking, then.

[per_funke]

[ This suggestion might classify as "off topic" depending on the degree of fundamentalism applied :0) ]

If you're just looking for the cheapest, still very effective, solution to microscope photography AND you're the owner of a smartphone maybe this can be a solution:
https://www.ebay.co.uk/itm/283012221033