Phototube options for Optiphot-2?

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Dubious
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Joined: Sun May 09, 2021 7:55 pm

Phototube options for Optiphot-2?

#1 Post by Dubious » Tue Jan 18, 2022 11:13 pm

My new Optiphot-2 (which I am coming to like) has the "T" trinocular head. I want to connect it to the full-frame Canon RP I also recently acquired, using a camera adapter from Newhoper or similar. The phototube that came with the Optiphot has a lens at the bottom so I think will not work (it was used with a CCD video camera adapter). I've just ordered a phototube from Ebay that looks to be standard (also ordered a CF PL2.5XA projection eyepiece). But now I notice that the "F" and "T" trinocular heads available for the Optiphot have about an inch height difference in the tube on top into which the phototube inserts. Do these heads take the same phototubes or is there a different series for each? Also, I found a reference stating that the "F" head gives the camera a straight path to the objective, i.e., without using the prism. Is that true and would it be an advantage? I had toyed with the idea of direct projection, but am not sure that is even possible, especially as I would like near parfocality with the objectives.

If anyone can shed some light on these things, it would be most appreciated.

PeteM
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Location: N. California

Re: Phototube options for Optiphot-2?

#2 Post by PeteM » Wed Jan 19, 2022 12:53 am

The "F" trinocular does have a straight path to the relay lens and also 100% of the light headed to the camera. One advantage is one less bit of glass in the way to gather dust. Another is a brighter image, for shorter exposure times or better frame rate on videos. The "T" head offers simultaneous viewing and partial light to the camera as an option - that could be handy for demos and classroom use if you're not using a monitor and live view to position and focus things.

My personal Optiphot-2 has an ergo (tilting) head and the flange to my camera (2.5x relay lens to full frame Nikon - should be about the same for you) is about 25cm above the top of the stand including the head. I end up making my own tubes for heads, once I figure the parfocal distance, so can't help you on which one you'll need for your F head. Many of the better generic ones will have some adjustment.
Last edited by PeteM on Wed Jan 19, 2022 12:59 am, edited 1 time in total.

Scarodactyl
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Re: Phototube options for Optiphot-2?

#3 Post by Scarodactyl » Wed Jan 19, 2022 12:58 am

edit: I was typing this before PeteM's comment went through, so it's partially redundant--sorry!
The heads all take the same adapters--the difference in height has to do with some internal lenses they put in the heads for whatever reason.
Direct projection is possible if you have a mirrorless camera and adapt it right onto the top of the photo tube*. you can try this by just holding it over the port.
That all said, I think for full frame using the 2.5x relay is a very solid option. If you find that direct projection is still of interest after trying the 2.5x you can start digging you way down that rabbit hole later. If I recall right the open diameter at the top of the head is 38mm, right? If so, you need a 38mm OD adapter that holds a 23.2mm eyepiece, then some way to mount empty spacers above to get the camera sensor the correct distance from the photo eyepiece to produce an image parfocal with the eyepieces. I don't remember if newhoper has a complete solution for that.



*that said depending on which head you have you still might need to modify it to avoid unnecessary cropping†

†and even then the widest field objectives in the lineup will cover aps-c and rarely much more so full frame would not be a great match‡

‡unless you then further paired it with a high quality 1.6x teleconverter, assuming that would actually fit into the provided space.

Dubious
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Joined: Sun May 09, 2021 7:55 pm

Re: Phototube options for Optiphot-2?

#4 Post by Dubious » Mon Feb 07, 2022 7:35 am

Thought I'd do an update on my attempt to connect the Nikon Optiphot-2 to a Canon RP mirrorless camera.

I initially had the Nikon T trinocular head with a phototube with a lens at the bottom, into which a CCD video camera adapter was inserted in place of a projection lens. I then acquired a Nikon F trinocular head with a phototube, into which a Nikon F camera adapter was inserted. Both of the phototubes had a sleeve for insertion of a photo projection lens. Neither of the phototubes would screw into the other head. I first tried to connect the camera using the Nikon F camera adapter (with a Nikon to Canon converter). Not very successful, as the base of the Nikon F adapter only fit around about the first 3/8" of the inserted PL2.5xa, meaning it could not fit inside the phototube at all, since the PL2.5xa extends about that much above the top of the phototube. BTW, the Nikon F adapter has a small lens above that point in its base (maybe its purpose is to correct the pincushion noted below?--I haven't yet put it back to check). I was able to use this combination by swapping an extra 10x eyepiece with the PL2.5xa, as the eyepiece is a lot shorter, allowing the Nikon F adapter to be inserted enough into the tube to clamp.

I achieved better results with a full-frame camera adapter I ordered from Newhoper (Ebay) to try in place of the Nikon F adapter. The Newhoper adapter works well with both the T and F heads. The Newhoper adapter has no lens near its base, so with the F head, which allows the trinocular tube to bypass the prism, the only glass between the objective and the camera is the PL2.5xa; however, the end result in terms of image quality seems the same with either head. Using an eyepiece in place of the PL2.5xa has the advantage that the diopter adjustment makes it easier to achieve parfocality with the eyepieces; however, I prefer the PL2.5xa, as it provides more light and better contrast. With both heads, there is just a bit of pincushion distortion, but overall I am quite satisfied.

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