Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Collimation of a Pentax 67 400mm EDIF camera lens

  • Please log in to reply
19 replies to this topic

#1 coinboy1

coinboy1

    Apollo

  • *****
  • topic starter
  • Posts: 1,424
  • Joined: 03 May 2011
  • Loc: Tulsa, OK

Posted Yesterday, 08:30 AM

Hello,

Recently acquired a Pentax 67 400mm EDIF camera lens off eBay. I have been wanting one of these lenses for a while now to try it out with astrophotography and I did last night with disappointing results. The stars are mis-shaped across the entire image. I think the collimation of one of the lenses is out of wack. Its not sensor tilt or image plane tilt, I tried inserting spacers at different points in the adapter bayonet with no luck on correcting it. I am pretty bummed...

 

Here is an example of the Vega starfield across an APS-C sized sensor from last tonight:

 

inspect.jpg

 

Essentially the out of focus star images look like this so I do believe it to be collimation and not camera tilt.

 

gallery_234528_9239_1614.jpg

 

Is there a way to check collimation of a lens by inserting a laser in the rear section? I was thinking I could 3D print a special adapter to my flange to get the laser dead center, I could also 3D print a center hole cover for the front aperture. I have never needed to collimation a refractor or camera lens before. The real question is whether my Pentax can be collimated...

 

Additionally I performed the DPAC test on this camera lens and the Ronchi lines show good correction inside and outside of focus and VERY smooth lines but the lines DID have a tilt or bow to them. I am thinking the optical axis is out of wack of one or more lenses.

 

IMG_1914.JPG

 

Here is my camera lens: 

 

s-l1600.jpg

 

Here is the internal lens configuration of the camera:

 

pentax400F4.jpg

 

Only hope is disassembly to figure how to collimate the lenses and to see what is wrong or return the lens. I bought it from a company that offers a 30day return period. I don't want to return such a beautiful lens but also don't know how the disassembly process would go...

 

Any advice or tips would be appreciated.



#2 chubster4

chubster4

    Explorer 1

  • *****
  • Posts: 89
  • Joined: 22 Jun 2012
  • Loc: Washington, D.C.

Posted Yesterday, 09:15 AM

No expert here, though most of my lenses back in the day were Pentax Takumars. 

Are there any exterior signs of impact, or barrels being out of round? It wouldn't take much in the way of mistreatment to slightly warp some component. Unless something (retaining ring?) is audibly loose, I would suspect this is the cause. I would return it and look for another.  


  • Matthew Paul likes this

#3 coinboy1

coinboy1

    Apollo

  • *****
  • topic starter
  • Posts: 1,424
  • Joined: 03 May 2011
  • Loc: Tulsa, OK

Posted Yesterday, 09:39 AM

No the exterior is excellent; doesn't appear to have ever been impacted by anything. There doesn't seem to be any visible slop or looseness anywhere. I am very tempted to remove the dew shield and dew shield attachment as I feel there may be adjustment screws under it. Also when I bought the lens the rubber grip looks like it has been removed before (see pic)

 

s-l1600 (1).jpg

 

After doing some research there is someone who disassembled their lens:

 

https://www.flickr.c...57644680739402/

 

Looks like there are some screws under rubber grip although his lens is a different model than mine.



#4 cuzimthedad

cuzimthedad

    Just Be Cuz

  • *****
  • Moderators
  • Posts: 6,650
  • Joined: 09 Apr 2006
  • Loc: Nampa, ID

Posted Yesterday, 10:12 AM

Moved to DSLR & Digital Camera Astro Imaging & Processing



#5 LarsMalmgren

LarsMalmgren

    Ranger 4

  • *****
  • Posts: 371
  • Joined: 22 Jan 2010
  • Loc: Denmark

Posted Yesterday, 11:03 AM

Moved to DSLR & Digital Camera Astro Imaging & Processing

Uhmm, but this is about fixing the lens, not using the lens !??


  • coinboy1 likes this

#6 coinboy1

coinboy1

    Apollo

  • *****
  • topic starter
  • Posts: 1,424
  • Joined: 03 May 2011
  • Loc: Tulsa, OK

Posted Yesterday, 11:51 AM

Agree thats why I posted in the ATM and optics form first.



#7 MKV

MKV

    Cosmos

  • *****
  • Posts: 8,841
  • Joined: 20 Jan 2011
  • Loc: Florida, USA

Posted Yesterday, 12:10 PM

Any advice or tips would be appreciated.

For one, I think it's not a good thing to test a lens in blue light unless it's design wavleneght was in blue close to your source wavlength. With mirrors, it's a different story. It helps to find the design wavelength of a lens system and use that wavelength for analysis.

 

Also, the results will vary for visual vs. photographic, as the distribution of color correction aims to satisfy the spectral profile of the intended use. For visual, the spectrum range is roughly between 481 and 658 nm, with the heaviest emphasis around 550-570 nm. Assigning proper wavelength "weight" to each wavelength in the analysis is also important for a more balanced idea of performance.

 

Axial coma is usually indicative of tilt or wedge. I have encountered that in some Surplus Shed air spaced objectives. 

 

SAM_4324LR (2).JPG SAM_4343_LR (2).JPG

 

Removing the wedge is often all that's needed.

 

SAM_4332_CR.JPG

 

Much worse is the appearance of axial astigmatism, which I have also, I'm sad to report, encountered in Surplus Shed lenses. 

 

on-axis astig.png

 

A generous return policy on purchased items is probably a good selling point but it should make a buyer wonder who owned the lens before and what was done to it. For high-tech items, I think it's best to buy directly from the manufacturer who is willing to guarantee the product and not just satisfaction.

 

Mladen


Edited by MKV, Yesterday, 12:15 PM.

  • coinboy1 likes this

#8 coinboy1

coinboy1

    Apollo

  • *****
  • topic starter
  • Posts: 1,424
  • Joined: 03 May 2011
  • Loc: Tulsa, OK

Posted Yesterday, 12:28 PM

Thanks Mladen for your insight. I agree blue light is not ideal, my Ronchi tester for my mirrors is blue and I need to order a white LED so I can separate out the Channels.

Looks like I might have some kind of misalignment in my camera lens. My choices are start disassembly or return it. My curious nature really wants to take it apart but once I do that I will void my ability to return. I am curious if there is an adjustment to fix the collimation of the lens cell.

#9 MKV

MKV

    Cosmos

  • *****
  • Posts: 8,841
  • Joined: 20 Jan 2011
  • Loc: Florida, USA

Posted Yesterday, 05:05 PM

Thanks Mladen for your insight. I agree blue light is not ideal, my Ronchi tester for my mirrors is blue and I need to order a white LED so I can separate out the Channels.

Looks like I might have some kind of misalignment in my camera lens. My choices are start disassembly or return it. My curious nature really wants to take it apart but once I do that I will void my ability to return. I am curious if there is an adjustment to fix the collimation of the lens cell.

I can totally relate to your curiosity, Tony! :o)  Generally, depending how much I paid for an item will determine my next step, he, he. Sometimes, tearing a piece apart for learning purposes is worth more than your money back! :o) It's your call.

 

For the light source, a super bright LED with dedicated narrow bandpass filters is ideal. This way you can test in bandwidths typically used in professional optics, such as 5461 (g line), and 532.8 (HeNe). Furthermore, such a beam can be collimated (made parallel) into a narrow pencil, and used instead of a laser diode without the annoying speckle.

 

This way you can use professional perfectly round and clean edge precision pinholes much smaller than the usual light source used by ATMs. Such small pinholes will reveal a lot more detail with a knife-edge test because you'll have maximum contrast.

 

You'll need some sort of a small x-y stage to center the pinhole on the beam. You may also use a microscope objective to focus the narrow pencil onto the the pinhole (spatial filter). This will not only give you a very bright spot, but also one that's free of undesirable optical "noise" -- a crispy "clean" signal.

 

unfiltered_vs_filtered_1.jpg

 

It's possible you could also use a single-pass optic fiber in place of a pinhole. Their core is usually only a few micros in breadth. That would make mounting the light source a lo lots easier because of obvious compactness of the configuration.

 

Narrow bandpass filters (abut 1 to 10 nm wide) are relatively inexpensive on eBay. Besides you'll need only a few dedicated wavlengths, so it shouldn't be a prohibitive expense to upgrade your testing. With a monochromatic light source you can advance to interferometry by building a point source interferoemter (no optics required), or a Bath interferometer, and then one day progress to a Twyman-Green, and finally to the more demanding and expensive such as the Schack cube, the Ceravolo IF, and other Fizeau-type instruments if you wish.

 

Mladen


  • coinboy1 and calypsob like this

#10 calypsob

calypsob

    Fly Me to the Moon

  • *****
  • Posts: 5,423
  • Joined: 20 Apr 2013

Posted Yesterday, 05:44 PM

I had wanted one of these for the longest time. Wei Hao Wang warned me that his copy was also de centered and I sort of lost interest. Im not sure who or how you can open this up and test, but based on some things I have read, all of the optics must be centered or the image can shift.

 

the people at lens rentals regularly break down lenses and have written some interesting information about decentered lenses. I almost wonder if you could pick their brain about this particular optic or maybe let them attempt to recenter it. 

 

If you do end up sending this back, there is a new 645 300mm EDIF, which does perform incredibly well - This version is black with a gold ring at the front.  Its probably in the same price range second hand, I have seen them on ebay under $1,500, new I think over $4k

 

https://wordpress.le...ets-a-makeover/

 

https://wordpress.le...-demonstration/

 

Also, here is a pretty interesting video showing how a cemeted doublet is optically aligned, not sure what that tool  is called though https://www.youtube....h?v=cl6K-EXPILo


Edited by calypsob, Today, 08:27 AM.

  • MKV and coinboy1 like this

#11 coinboy1

coinboy1

    Apollo

  • *****
  • topic starter
  • Posts: 1,424
  • Joined: 03 May 2011
  • Loc: Tulsa, OK

Posted Yesterday, 08:02 PM

Thanks Wes! Incredibly good information in those links. I will set up some tests charts now!


  • calypsob likes this

#12 whwang

whwang

    Gemini

  • *****
  • Posts: 3,174
  • Joined: 20 Mar 2013

Posted Yesterday, 08:08 PM

Please do let us know if you find ways to fix it. Like Wes said, I encountered quite a few old Pentax (67 and 645) lenses that show similar problems. My general conclusion is that film does not require very good optics comparing to today’s digital sensors, so the manufacturing accuracy wasn’t that high at that time. If there is a way to fix such miscollimation and tighten it up, it will help to bring many old lenses back to life.
  • calypsob likes this

#13 MKV

MKV

    Cosmos

  • *****
  • Posts: 8,841
  • Joined: 20 Jan 2011
  • Loc: Florida, USA

Posted Today, 12:22 AM

not sure what that tool  is called though https://www.youtube....h?v=cl6K-EXPILo

Chopstick? :o) 



#14 MKV

MKV

    Cosmos

  • *****
  • Posts: 8,841
  • Joined: 20 Jan 2011
  • Loc: Florida, USA

Posted Today, 01:46 AM

My general conclusion is that film does not require very good optics comparing to today’s digital sensors, so the manufacturing accuracy wasn’t that high at that time.

That's not exactly true. Superachromats were invented in the early 1960's (using the theory of Max Herzberger). The Zeiss West Germany was producing highly corrected astrographs a in the '60s and '70s, and even on the amateur level fixed focal length telephoto lenses for 35 mm film frames (43 mm diagonally) were capable of delivering astrophotos.

 

I used an Olympus OM-1 mirror camera specifically designed for astronomical and micvorsopic work. You you would lift the mirror manually and only the shutter open, thus eliminating any vibration.

 

For astrophotos, I was using Al Jaegers' 3 and 5 inch f/5 RTF telescopes with filter for stunning deep sky images in red, and for really wide field a Spiratone (pretty much a bargain basement lens) 135 mm f/1.8!!! telephoto with an 82 mm red filter for objects such as the North America and Veil Nabulae, etc.

 

Don't forget state of the art Questar was being manufactured back in the 1950's!

 

None of them had coma in the center of the lens. I would say that despite much advanced technology in the 21st century the quality of work is way down, even shabby, compared to the things of yore. 

 

Images:

 

(1) My Jaegers tandem 3 and 5 inch f/5 with 2.75" standard Jaegers focuser, on a Jaegers mount, Jaegers rings, and RA drive. This was all standard equipemnt and non plastics! The declinaiton drive is a DIY DC stepper motor.

 

5in Jagers_LR.jpg

 

(2) The Spiratone 135 mm f/1.8 "portrait lens" with a full aperture red filter for deep sky nebulae.

 

20200803_014604_LR.jpg 20200803_014743_LR.jpg

Attached Thumbnails

  • 20200803_014633_LR.jpg


#15 calypsob

calypsob

    Fly Me to the Moon

  • *****
  • Posts: 5,423
  • Joined: 20 Apr 2013

Posted Today, 08:29 AM

Chopstick? :o) 

Lol chopstick and a dial indicator, thats all you need!

 

Do you happen to know what that z axis contraption is called that emits the beam through those lenses?



#16 calypsob

calypsob

    Fly Me to the Moon

  • *****
  • Posts: 5,423
  • Joined: 20 Apr 2013

Posted Today, 08:38 AM

That's not exactly true. Superachromats were invented in the early 1960's (using the theory of Max Herzberger). The Zeiss West Germany was producing highly corrected astrographs a in the '60s and '70s, and even on the amateur level fixed focal length telephoto lenses for 35 mm film frames (43 mm diagonally) were capable of delivering astrophotos.

 

I used an Olympus OM-1 mirror camera specifically designed for astronomical and micvorsopic work. You you would lift the mirror manually and only the shutter open, thus eliminating any vibration.

 

For astrophotos, I was using Al Jaegers' 3 and 5 inch f/5 RTF telescopes with filter for stunning deep sky images in red, and for really wide field a Spiratone (pretty much a bargain basement lens) 135 mm f/1.8!!! telephoto with an 82 mm red filter for objects such as the North America and Veil Nabulae, etc.

 

Don't forget state of the art Questar was being manufactured back in the 1950's!

 

None of them had coma in the center of the lens. I would say that despite much advanced technology in the 21st century the quality of work is way down, even shabby, compared to the things of yore. 

 

Images:

 

(1) My Jaegers tandem 3 and 5 inch f/5 with 2.75" standard Jaegers focuser, on a Jaegers mount, Jaegers rings, and RA drive. This was all standard equipemnt and non plastics! The declinaiton drive is a DIY DC stepper motor.

 

attachicon.gif5in Jagers_LR.jpg

 

(2) The Spiratone 135 mm f/1.8 "portrait lens" with a full aperture red filter for deep sky nebulae.

 

attachicon.gif20200803_014604_LR.jpgattachicon.gif20200803_014743_LR.jpg

Modern lenses contain lots of glass fiber plastics, mostly for thermal properties. They are definitely not the tank lenses of the 60’s, some still are but its unusual.  The abundance of ED glass and high tech AR coatings however make it possible to image wide open on some modern lenses, which is pretty phenomonal. There are only a few vintage lenses that can do this, zeiss 60mm f4 s-ortho for example.



#17 MKV

MKV

    Cosmos

  • *****
  • Posts: 8,841
  • Joined: 20 Jan 2011
  • Loc: Florida, USA

Posted Today, 12:20 PM

Do you happen to know what that z axis contraption is called that emits the beam through those lenses?

Not a clue. :o)

 

However, it must be some type of a vertical autocollimator ( https://www.vermontp...es-autocoll.png )



#18 MKV

MKV

    Cosmos

  • *****
  • Posts: 8,841
  • Joined: 20 Jan 2011
  • Loc: Florida, USA

Posted Today, 12:24 PM

Modern lenses contain lots of glass fiber plastics, mostly for thermal properties. They are definitely not the tank lenses of the 60’s, some still are but its unusual.  The abundance of ED glass and high tech AR coatings however make it possible to image wide open on some modern lenses, which is pretty phenomonal. There are only a few vintage lenses that can do this, zeiss 60mm f4 s-ortho for example.

Oh agreed, it's just that it's not true that "manufacturing accuracy wasn’t that high at that time.."  Modern digital photography is unbelievable -- today small apo refractors take pictures one could only dream of taking  with a small aperture a few decades ago.  



#19 MKV

MKV

    Cosmos

  • *****
  • Posts: 8,841
  • Joined: 20 Jan 2011
  • Loc: Florida, USA

Posted Today, 12:28 PM

Let's not forget the first lithographic lens was manufactured in 1977. Tolerances for such lenses are in ppm (part per million).



#20 whwang

whwang

    Gemini

  • *****
  • Posts: 3,174
  • Joined: 20 Mar 2013

Posted Today, 09:21 PM

I was talking about Pentax lenses based on my own experience, which happens to match what the OP found.  Other brands? No comments.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics