Narrowband with a vintage lens?

[Space_Plane]

Hi all,

Was hoping for some quick info / opinions on taking e.g. H-alpha frames with a mono camera, but using a vintage lens.  Does it work well?  Any focus issues / general problems?  Advice?  Examples? etc etc 

I ask as i've been experimenting with a vintage pentax 135mm lens, but using an OSC cooled camera. 

I got less than useful results with both an l-enhance / l-pro filter, failing completely to get all channels to focus together, no matter what.  

See attached gif cycling between blue and red channels.  Does using mono / narrowband "sidestep" this issue, as i'm no longer trying to focus 3 colours?

Hope that makes sense!

Cheers

Chris

[Xiga]

25 minutes ago, Space_Plane said:

Hi all,

Was hoping for some quick info / opinions on taking e.g. H-alpha frames with a mono camera, but using a vintage lens.  Does it work well?  Any focus issues / general problems?  Advice?  Examples? etc etc 

I ask as i've been experimenting with a vintage pentax 135mm lens, but using an OSC cooled camera. 

I got less than useful results with both an l-enhance / l-pro filter, failing completely to get all channels to focus together, no matter what.  

See attached gif cycling between blue and red channels.  Does using mono / narrowband "sidestep" this issue, as i'm no longer trying to focus 3 colours?

Hope that makes sense!

Cheers

Chris

Hi Chris

Have you tried stopping the lens down at all? I am guessing you are trying it wide open, although even then the disparity in focus in the gif is pretty huge. What exact lens are you using? Some vintage lenses are ok, but most are not great by today's standards. 

If the lens is ok, you can get some pretty decent images with mono and NB. I recently had a go at this myself, using an old Tamron 135mm F2.8. It needs stopped down to at least F4 though. As long as your lens doesn't have any serious issues like astigmatisms, then stopping down should work. 

I've only had two outings with my setup, I've posted links to them below. The 1st was just a test session, and the 2nd is a WIP project to capture Cygnus in SHO.

HTH.

 

[Space_Plane]

Hi Ciaran, many thanks for your reply.  Your images look great!

The lens is an SMC Pentax 135mm F/2.5 (K-mount), and truthfully I was expecting a bit better from it lol.

The gif above was at ~ F/3.6 using step-down rings infront of the lens, but I tried it systematically all the way down to F/8.  It really didn't improve it all that much, but even if it had, I wouldn't overly want to bother using it that slow.

Hopefully the lens doesn't have any other serious problems, hard to tell with the focus issues, but good to know it could potentially work better with mono, thanks for that  

I've already wasted one rare clear night experimenting with this, so it looks like it could be more!  The only mono camera I have (currently) is a little 120mm-mini, so I'm going to rig some sort of frankenstein's monster of an adapter to use it with this lens, before I would consider any further purchases!

Thanks again

Chris

[DaveS]

I think it would work very well in NB with a filter wheel provided you remembered to refocus between filters or had some kind of autofocus attachment.

At least one of us here @Gina uses "vintage" lenses (M42, older than K-mount) very successfully in a dual rig.

[Gina]

I get excellent results using narrowband filters with Asahi (Pentax) Takumar, Super Takumar and SMC Takumar M42 mount lenses.  These are superb lenses and work well even at full aperture.  I have several of various focal lengths.  The point with terrestrial camera lenses is that they are not fully APO into the deep red but with very narrow band filters this isn't a problem - just that you need different focus settings for Ha & SII as compared with OIII.

HTH.

[rotatux]

3 hours ago, Space_Plane said:

gif above was at ~ F/3.6 using step-down rings infront of the lens

IMO You should instead really try stopping down with the lens' own diaphragm : I have tried step-down rings too, surely they cut down on light (affect aperture geometrically, if I can say like this) but mostly don't enhance optical properties as much as the native diaphragm (I was still having coma and CA in sides and corners, shooting RGB on OSC camera)

[Space_Plane]

Hi @DaveS, @Gina, @rotatux,

Thanks very much for your additional info & comments regarding focus / step down, shall keep them in mind!  Certainly good to know in the end that the lens might not be a complete waste if used with mono.

Look forward to testing it with what I have, got to figure out some more adapters etc first and take it from there 

Cheers

Chris

[8472]

On 07/09/2020 at 12:13, Gina said:

I get excellent results using narrowband filters with Asahi (Pentax) Takumar, Super Takumar and SMC Takumar M42 mount lenses.  These are superb lenses and work well even at full aperture.  I have several of various focal lengths.  The point with terrestrial camera lenses is that they are not fully APO into the deep red but with very narrow band filters this isn't a problem - just that you need different focus settings for Ha & SII as compared with OIII.

HTH.

Hi Gina

I also have 55mm Super, 135 and 200mm M42 SMC Takumar lenses I'm thinking of pairing with my 294M.

Do you have any experience of using these wide open with M4/3 or larger mono sensors?

In my experience they only work acceptably when stopped down to at least F/5 with OSC, so I'm reluctant to waste the few clear spells we have imaging too wide open.

Thanks