Good M42 lenses for widefield?

[badgerchap]

D'oh! Only just discovered that screw on lenses will fit my 10D with the t-mount adapter!

The question now then is:

What focal length to get for widefield, the Milky Way in particular?

I have a 200mm f3.5 but I don't reckon that's really going to do it.

Any ideas?

[davew]

Either I'm not understanding what you're saying or you have the wrong ideas.

An M42 lens will not fit a T mount. Well, not unless you wreck the threads. Different pitch so please don't try it

Plus the registration distance for M42 is 45.5mm and T mount is 55mm. You need an adapter for M42.

Once you have the correct adapter try your lens. It may work.

Dave.

[badgerchap]

Forgive me, it's my nomenclature which is out, not the adapter! Whatever it's proper name is, it connects my M42 200mm lens (an old Chinon from circa 1970) to the EF fitting on the DSLR. Fits perfectly, with no wrecking of threads (except this one )!

[Dodge]

I like the old Russian Jupiter M42 lenses, cheap and decent quality.

[JamesF]

Gina has done a fair bit of experimentation with M42 lenses. She should be able to offer some opinions I'm sure.

James

[michael.h.f.wilkinson]

The best 50 mm p-thread (as it was called, indeed a different pitch to t2-thread) lens is without a doubt the Pentax Super Takumar 1.4/50mm, not easy to come by but if you can grab it. I think there were also F/1.8 version which were very good . The Helios F/2 58mm (used on Zenith cameras) is a clone of the pre-war Zeiss Biotar of the same specs, and can be quite good, especially given the low price. Yashica also made some very passable 1.7/50 or 1.8/50 in M42, before they switched to Contax/Yashica bayonet.

[badgerchap]

Thanks Michael, I'll keep an eye out. Fleabay looks like a half decent source, at least for some of those

[Ewan]

I have a couple in my sig, a Asahi f2 50mm & Super Takumar 55mm f1.8, both very good for widefield but now i have used them i feel they could be wider but they are quality.

[themos]

You'll always battle chromatic aberration with old M42 lenses.

[Ewan]

I do get coma but found stepping down a notch or 2 worked well, image wise i think they are great & if you are new to lenses don't go & blow a fortune on something you may not need or is not quite suitable, for what they cost get some cheap M42's & have a bash.

Still learning myself tbh & at the monent i am on the lookout for a nice 400mm

[badgerchap]

Yes I've already noticed the CA on terrestrial targets. Like you say though it's mainly a way to get used to things before I shell out for something expnsive.

[Gina]

Gina has done a fair bit of experimentation with M42 lenses. She should be able to offer some opinions I'm sure.

James

Yes, I have quite a collection of lenses Firstly, these are M42 x 1mm thread known as Pentax/Praktica thread. Not to be confused with the M42 x 0.75mm thread that is T2. Same diameter but different thread pitch. I used these lenses because I already had several from my film days. I have been interested in photography since my Dad introduced it to me when I was very young. I started with a Box Brownie in the early 1950s and moved up the scale getting to a Pentax Spotmatic SLR camera. This came with a 55mm f1.8 lens. I added various other lenses such as a wide angle 35mm f3.5, telephoto 135mm f2.8 and a 35-105mm zoom. The genuine Pentax lenses made by the Asahi Optical Co. of Japan and called Super Takumar and later SMC Takumar (meaning Super Multi Coated) were and still are excellent pieces of glass.

Having been into astrophotography with a scope, I thought I'd try these lenses for imaging the wider DSOs as some other members had done with success. I bought several by auction on ebay at very low prices - other makes at first and then moving up the the more sought after SMC Takumars. One I've used a lot is the 200mm f4 and recently I've added the 105mm f2.8 to bridge the gap between the 55mm and the 200mm. The 135mm lens I used for photography was a cheapo and had a very stiff focussing sleeve so I've not used this for imaging. ATM I'm using it with an 1100D as an electronic finder.

To use these lenses with the Canon EOS series DSLRs is simply a matter of buying a cheap adapter (but make sure you get one that guarantees infinity focus). You can also get adapters for some other makes of DSLR but Canons are the best supported for AP.

I'm now using these lenses with my astro CCD - a mono 314L+ with filters in the Atik EFW2 filter wheel. Again an adapter is used to connect the lens to the T2 adapter from Atik for the EFW2. Focussing actually covers more than infinity and I'm using a 1.2mm delrin spacer on one of the threads. The M42x1mm to T2 adapter is called a "Russian Adapter" and available from TS and the Atik T2 to M54 is available from FLO.

HTH but if there's anything else anyone wants to know I may be able to help.

[badgerchap]

Thanks Gina, lots to think about there, although doubtlessly this will end up costing - not least because you've just planted the seed of the isea of fiddling with my qhy5v and a lens, could be a laugh!

[Gina]

Now to Ca - Chromatic Aberration. This occurs where light at different wavelengths converges at different distances from the lens. The result is that if you focus one colour light you find it out of focus for a different colour. Photography lenses are only partly corrected for CA. Manufacturers rely on a property of the human eye and brain that slightly out-of-focus red is not noticed as much as green or blue. Most normal photo subjects have little red in them and as long as the green and blue parts of the spectrum are sharp the whole picture looks sharp. So they correct the green and blue very well but the red less so and save costs. Lenses of this sort are called achromatic whereas lenses corrected for the full visual spectrum are called apochromatic. Same applies tp refracting telescopes - the cheaper ones don't get the full CA correction - achromats. OTOH the apochromats are fully corrected over the entire visual spectrum.

Why is this important? Well, in imaging stellar objects there is a considerable amount of light at the red end of the spectrum. The most common elenent is hydrogen and whne this is energised by radiation from nearby stars it glows with a predominantly red light - called hydrogen alpha. It also produces a smaller amount of blue light call hydrogen beta. Being only about a quarter of the Ha this other radiation is generally ignored. Of course, there is not only red Ha light but other colours too, particularly in galaxies, for instance. So we need to allow for light of all visible wavelengths (I'm not considering specialist AP of infra-red or others here). This is of most consequence with colour sensors where all the colours are exposed at the same time though in reality it doesn't appear as bad as one might expect - after all the final image is still being viewed by human eyes and brain.

Where filters are used to pick out certain wavelengths of light such as narrow band or RGB these different colours need focussing differently. As long as the image is refocused for each filter, CA can be overcome.

I think that pretty much covers it but I've probably missed something

[badgerchap]

Nice explanation of CA there Gina thanks

[Ewan]

Yes, I have quite a collection of lenses Firstly, these are M42 x 1mm thread known as Pentax/Praktica thread. Not to be confused with the M42 x 0.75mm thread that is T2. Same diameter but different thread pitch. I used these lenses because I already had several from my film days. I have been interested in photography since my Dad introduced it to me when I was very young. I started with a Box Brownie in the early 1950s and moved up the scale getting to a Pentax Spotmatic SLR camera. This came with a 55mm f1.8 lens. I added various other lenses such as a wide angle 35mm f3.5, telephoto 135mm f2.8 and a 35-105mm zoom. The genuine Pentax lenses made by the Asahi Optical Co. of Japan and called Super Takumar and later SMC Takumar (meaning Super Multi Coated) were and still are excellent pieces of glass.

Having been into astrophotography with a scope, I thought I'd try these lenses for imaging the wider DSOs as some other members had done with success. I bought several by auction on ebay at very low prices - other makes at first and then moving up the the more sought after SMC Takumars. One I've used a lot is the 200mm f4 and recently I've added the 105mm f2.8 to bridge the gap between the 55mm and the 200mm. The 135mm lens I used for photography was a cheapo and had a very stiff focussing sleeve so I've not used this for imaging. ATM I'm using it with an 1100D as an electronic finder.

To use these lenses with the Canon EOS series DSLRs is simply a matter of buying a cheap adapter (but make sure you get one that guarantees infinity focus). You can also get adapters for some other makes of DSLR but Canons are the best supported for AP.

I'm now using these lenses with my astro CCD - a mono 314L+ with filters in the Atik EFW2 filter wheel. Again an adapter is used to connect the lens to the T2 adapter from Atik for the EFW2. Focussing actually covers more than infinity and I'm using a 1.2mm delrin spacer on one of the threads. The M42x1mm to T2 adapter is called a "Russian Adapter" and available from TS and the Atik T2 to M54 is available from FLO.

HTH but if there's anything else anyone wants to know I may be able to help.

Yes Gina, it's because of that 200 F4 you bought that i started collecting more glass, what have you started

I know my kit lens is 18mm but it's still a fairly cheap lens & i already prefer the Asahi 50mm & 55mm.