Cost effective prime lenses for wide field imaging

[Stub Mandrel]

I have two 58mm Helios and a 28mm Sirius M42 fit lenses. Both of these show stretched stars in the corners, even when stopped down considerably.

Can people offer some examples of cost effective secondhand lenses for widefield imaging. Ideally with image examples to show how sharp they are across the image.

Low cost is important as they may need to be 'hacked' to reach focus with my modded DSLR. I understand that AF lenses usually have the extra mm or so of travel to reach focus with a modded DSLR in manual mode - is this correct?

Thanks!

[MARS1960]

1 hour ago, Stub Mandrel said:

I have two 58mm Helios and a 28mm Sirius M42 fit lenses. Both of these show stretched stars in the corners, even when stopped down considerably.

Can people offer some examples of cost effective secondhand lenses for widefield imaging. Ideally with image examples to show how sharp they are across the image.

Low cost is important as they may need to be 'hacked' to reach focus with my modded DSLR. I understand that AF lenses usually have the extra mm or so of travel to reach focus with a modded DSLR in manual mode - is this correct?

Thanks!

Yes it's correct.

I had one of these for a while, an impressive lens for peanuts, sorry no pics.

https://www.ebay.co.uk/itm/Carl-Zeiss-Jena-MC-f3-5-135mm-Sonnar-Prime-Portrait-Lens-M42-Screw-Fit-or-DSLR/253977412049?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D55149%26meid%3Dd8ad8743ad1141d6b00669dc22f3b13e%26pid%3D101006%26rk%3D1%26rkt%3D1%26%26itm%3D253977412049&_trksid=p2045573.c101006.m3226

[Stub Mandrel]

Thanks Mark,

I already have a 135mm Zeiss Sonnar, I got it in the mid 1980s! Unlike my shorter lenses it does indeed give pin-sharp stars across the image.

I'm hoping for shorter lenses that can give me similarly impressive results!

[michael.h.f.wilkinson]

The Pentax SMC 50 mm F/1.4 m42 thread has a good reputation. Never used one, however.

[Stub Mandrel]

Thanks Michael. I wonder how the Pentax 1.8 compares.

The stock Canon 50mm f1.4 sounds useful and affordable but corners are poor unless stopped to 2.8.

[coatesg]

3 hours ago, Stub Mandrel said:

Low cost is important as they may need to be 'hacked' to reach focus with my modded DSLR. I understand that AF lenses usually have the extra mm or so of travel to reach focus with a modded DSLR in manual mode - is this correct?

Does depend a little on how the DSLR was modded - my 350d initially just had the blocking filter removed when I got it. It's fine for scope work, but no lens would come to focus. Solution was to add the Baader BCF in place (with a little silicon sealant...) and everything now is fine. 

I picked up a nice 85mm f1,8 Canon prime on ebay - but it needs to be stopped down to at least f4 to perform well enough for me. The 200mm L  is much more expensive but sharper - even then needs almost f4 to be acceptable. 

[Stub Mandrel]

Thanks Graeme

It's focal lengths of 50mm and less I am particularly interested in.

[happy-kat]

I'm pleased with the old super takumar f2 50mm (might be 55mm it is in the garage) it is quite good wide open I've uploaded images from it before but I'm on tablet so can't add to thread now) it was less than £30 from memory. The CA is minimal unlike my helios f2.8 135mm but that is quite good on corners too. Neither are probably not as good as your samyong 135mm.

My cosima 28mm is rather poor so I'd avoid one of those.

Either m42 or p k mount.

[Stub Mandrel]

Thank's that's one to consider ?

[Alien 13]

Its difficult to suggest a lens for a modded camera as most will give problems with star bloat unless you use a suitable clip in filter, this makes any EF-S type lenses incompatible which is a shame as the std kit 18-55mm lens is actually very good although a bit slow. The 50mm and 40mm STM lenses might be worth a try.

Alan

[happy-kat]

The 40mm pancake benefits I think from stopping down to f4.

[Alien 13]

37 minutes ago, happy-kat said:

The 40mm pancake benefits I think from stopping down to f4.

I think thats true of most/all lenses apart from the mighty Samyang 135 f2 which likes to be run wide open, odd thing is the native Canon f/4 lenses (the L type) also are happy at f/4 while the faster versions have to be stopped down to guess what..... f/4.

Alan

[happy-kat]

This is a single 180 second exposure Canon 1100d super takumar lens ISO 800 (it is not the SC variant) either wide open or was f2.8. Maybe it is not good enough in the corners for you (some might be also down to my tracking and/or polarv alignment on the barn door). Member Rotulux (similar name) had been testing the various 50mm vintage lens he had picked up to see whether any where good or not.

[Stub Mandrel]

10 minutes ago, happy-kat said:

Maybe it is not good enough in the corners for you (some might be also down to my tracking and/or polarv alignment on the barn door).

It's not perfect, but better than I'm getting. I could correct that with the lens correction in Pant Shop Pro followed by a light crop.

This is what I get at the moment:

58mm Helios on modded camera, bodged to focus OK and iris forced to (you've guessed it) about f4, nor quite as bad as I remember although the corner star shapes are poor (astigmatism and coma in corners are terrible wide open at f2 and bigger stars get stretched horribly):

This is the helios corrected in Photoshop and hefty crop of curved edges left after correction. Misses the point of having a wide angle to lose so much, plus I guess this is distorted too much for a mosaic.

28mm sirius on unmodded camera, you can see it's quite bad:

[happy-kat]

Maybe I should try the Takumar at f4 just to get an image to compare with for this thread. The Sirus lens I see what you mean. I wonder if the Cosima is that bad I just remember the CA rather than coma, might have to fish around images to see what I might have.

[Stub Mandrel]

I've thinned down an M42 adaptor as an experiment, now I can look at getting M42 or T-mount lenses without having to bork them to get focus.

 

[happy-kat]

The pancake 24mm is on offer at curries for £79 today

[chiltonstar]

I use a Nikon f2.8 28mm AIS, bought for £100.

Image example at f2.8, whole field - sorry about the processing, but I'm mainly visual.

Chris

[fwm891]

What's the 'hack' your doing? If your changing the back focus then that is probably why your not getting clean stars in the corners even when stopped down.

[Stub Mandrel]

1 hour ago, fwm891 said:

What's the 'hack' your doing? If your changing the back focus then that is probably why your not getting clean stars in the corners even when stopped down.

Various things like removing stops or moving the focus thread around by one start so the lens can move inwards further, no change to the optics.

[Alien 13]

4 hours ago, Stub Mandrel said:

I've thinned down an M42 adaptor as an experiment, now I can look at getting M42 or T-mount lenses without having to bork them to get focus.

 

Good idea but I have noticed that a lot of M42 lenses dont sit flush with the standard ring and so you can sometimes get enough inward movement by just removing material from the inner edge of the ring,

Alan

[happy-kat]

I was beginning to feel maybe the 24mm f2.8 was tempting me then I started to read this link here and though maybe 8.5mm and smaller was just too tiny a clear aperture size (still reading though to ensure whether it counts or not).

[Stub Mandrel]

1 hour ago, Alien 13 said:

Good idea but I have noticed that a lot of M42 lenses dont sit flush with the standard ring and so you can sometimes get enough inward movement by just removing material from the inner edge of the ring,

Alan

Useful to know, Alan, thanks.

[Stub Mandrel]

44 minutes ago, happy-kat said:

I was beginning to feel maybe the 24mm f2.8 was tempting me then I started to read this link here and though maybe 8.5mm and smaller was just too tiny a clear aperture size (still reading though to ensure whether it counts or not).

I doubt I would bother without tracking so even f2.8 seems lightning fast to me ?

[Stub Mandrel]

The canon 18-55 isn't a prime but seems to be highly rated and is dirt cheap s/h... about £30 for a scruffy one including p&p.