Canon 40mm pancake lens AP

[Stefan Buda]

Has anyone tried one of these lenses, with APS size sensor, for astrophotography? The reviews say that it is a sharp lens.
I've just bought one and intend to pull it apart and convert it to manual focusing.

[leon]

Yes I have used one many years ago, and gave it back to my mate at Camera House, did not like it at all.
But it was not one of the newer versions, the truth be known I think mine was about 20mm but very basic.
Actually now that it comes to mind, I recall it being for a Pentax :shrug:but i did use one once :lol:

Leon :thumbsup:

[Stefan Buda]

Thanks Leon,
I chose the 40mm version because it seems to be superior to the other Canon pancake lenses.
Stefan

[bojan]

Stefan,
Long time ago I used SMENA-8 as astrocamera, and I still have that lens somewhere, it is 40mm, f4. It was quite sharp, even in corners of 24x36mm film, so it may be quite OK for APS sensor. I will try to find it in my crap-yard and send it to you, it wouldn't be too difficult to make 3D printed adapter for EOS (hopefully it won't interfere with camera mirror...)

EDIT:
OK, I just saw you bought one...
But I will still experiment a bit with mine (when weather permit) and let you know..

[Stefan Buda]

Bojan,
I thought that this may be a lens that was designed for digital cameras, but I could be wrong and it is a revamped old design from the film era.
Film era lenses, in my limited experience, seem to suffer from poor correction at the red end of the visible spectrum. Film, both colour and b/w, used to have a sharp drop-off in sensitivity in the red.

[acropolite]

The 40mm pancake is an f2.8 lens not F4, it is a new design and as stated reported to be very sharp. Not sure why you would want to mod it for Manual focus as it already has manual focus, it's just that the manual focus is electronic rather than mechanically coupled. I use one on my 6D, although have not pointed it skyward.

[JA]

Hello SB,
Here is a review with resolution tests etc.. it seems to perform well:
http://www.lenstip.com/343.4-Lens_review-Canon_EF_40_mm_f_2.8_STM_Image_reso lution.html

Best
JA

[pluto]

I used this lens a bit when I had my 5DmkII and it was a real surprise for AP in my opinion. Pretty sharp with very little CA even wide open. On a full frame sensor it did deteriorate towards the edges but I think on an APS-C sensor you'd get a great image across the whole frame.
I still think it's one of the best lenses I've used for widefield AP, the only down side is that it's all motorised focus and so focusing can be a bit of a pain.

If I had an EF to Sony E adapter with all the electronics I'd still be using it with my A7s.

Leon, if you had a Canon 20mm pancake then that's designed for their smaller mirrorless cameras, like the "M" series. It might work with an APS-C DSLR but I can't imagine the quality would be any good. Different species to the 40mm.

[Regulus]

I haven't used one, but have read the reviews and it get's very high marks for sharpness across the field.
I would be interested to see the end result of you conversion, and a few pictures of the process Stefan.

Trev

[Stefan Buda]

Phil,
I should have explained that I don't use DSLRs. I don't like them because they are such a 20th century pain, with flip mirrors, ISO settings etc. Hope they will go extinct soon.
So I want to mount this lens on my QHY8 and that is why it needs real manual focus.
JA,
Great link, thanks. Looks like I made the right choice.
Hugh,
Thanks for the feedback. Sounds like I'm on the right track.
Trevor,
Yesterday I ripped out (literally) all the unnecessary parts and turned a jig with an M52x0.75 male thread that allowed me to screw on what remained of the lens assembly and spin it in the lathe to check lens alignment. All that I ended up keeping was the front of the "lens" with the housing of the optics including the iris mechanism. The rest of the mechanical parts, made of plastic, had too much runout for my liking.
I will make a metal back side with a Pentax screw mount and locking ring so that I can interface it to my CCD.

Stefan

[pluto]

This lens doesn't focus without power as there is no direct mechanical connection from the focus ring to the focusing mechanism.
But reading the rest of your previous comment it sounds like you're accessing the focusing mechanism directly...?

[Stefan Buda]

I discarded the focusing mechanism, the electronic controls and the back end with the bayonet mount. My focusing will be done with the screw mount and locked into place by a locking ring. It only needs infinity focus and I doubt that it will need to be refocused due to temperature changes.
The iris will be set permanently to whatever opening I find acceptable.

[pluto]

Sounds interesting. I'd love to see some photos of it, and from it, when you're done!

[Stefan Buda]

I'm using only the top left assembly and the front cover.
I'll post more pics when I'm done with the new housing.

[Stefan Buda]

And here's the new back end for the lens. All I need to do now is to 3D print a light baffle and take it to VicSouth for a test.

[Stefan Buda]

I tested the lens at VicSouth and I'm quite happy with it.
The brighter stars are a bit squashed near the corners of the field but show no "wings" or flares. Also there is just a bit of field curvature as the centre is a bit soft when the corners are well focused. I had the iris closed by about half a stop. Next time I will try it about one full stop down, at f/4.

[Regulus]

This is a cool project Stefan and has started me thinking regards som old lenses I have.
Thanks for the idea mate.
The reviews showed a good result at max aperture, bit perhaps terrestrial subjects are a bit diferent. I hope that f4 is as far as you have to go to get the result. It'd be a shame to lose light.
Trev

[bojan]

Trevor,
I found out that (modified to EOS) Canon 50mm f/1.4 (@ f/3.5) is excellent.
Also Canon FD 100mm F/2.8 (@f/4), it has a bit of lateral CA but this is easy to fix with PTLens.

Tair 11A (135mm F/2.8) is also extremely sharp at centre, but it has some coma in corners (but no visible CA)
Definitely worth a try, if you have them already.

[Regulus]

What really kicked the ball off for me Bojan was these 2 Youtube videos. I hadn't even considered conversions because we all know Canon don't give a rats about their old customers. They just want them to spend more money.

https://www.youtube.com/watch?v=0ndq7Fw81Lw

https://www.youtube.com/watch?v=9nXQBcyAjik

In the end I decided 'Why not'. The lenses are useless to me otherwise.

Trev

[bojan]

Trevor,
Have a look here (http://www.iceinspace.com.au/forum/showthread.php?t=39293&highlight=canon+50mm+EOS).. This is how I modified my FD 50mm, 100mm, 200mm, 300m...
400mm FD was more complicated, but it was the same procedure in principle.