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Pentax 645 300 mm ED f/4 lens


Astrofriend

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I bought another 300 mm lens as an alternative to the Canon 300 mm L lens I already have. The main reason is to achive a lower vignetting. I have very positive experience from an earlier medium format lens. This is the Pentax 645 300 mm ED f/4 lens with good reputation. If I get some positive results from this lens I maybe replace my Canon 300 mm lens with this one.

Here is some photos and data about the lens:
http://www.astrofriend.eu/astronomy/projects/project-pentax645-300ed/01-pentax645-300ed.html

I bought it mostly because I'm curious about it and want to test it. It's more than ten years older than the Canon lens.

Lars

Edited by Astrofriend
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  • 1 month later...

My Canon 300 mm lens setup is ready for some test in the night, I have already done some test in the opening of the clouds and could see that it works very good.

 

Now I planning for my next 300 mm lens, the Pentax 645 medium format f/4 ED lens. The last days I have 3D-printed two tube rings. It feels very stable and I hope it will not fall apart during the night.

 

This is how they look:

http://www.astrofriend.eu/3d-printing/pentax645-300mm-bracket/01-pentax645-300mm-bracket.html

 

Only the 180 teeth pulley missing for the motor focus.

 

/Lars

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  • 2 weeks later...

First light with the Pentax 645 300 mm ED f/4 lens.

http://www.astrofriend.eu/astronomy/astronomy-photo/galaxies/m101/m101-galaxy.html

Click on the image to bring up the full resolution image and inspect the corners. Look very good to me except one of the corner.

This old medium format lens is impressive. There are not many old cheap medium format lenses with ED glass elements, they are too old for that. The never APO medium format lenses are very expensive and have electronic aperature and focus which can be complicated to use in an astrosetup.

/Lars

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7 minutes ago, Astrofriend said:

First light with the Pentax 645 300 mm ED f/4 lens.

http://www.astrofriend.eu/astronomy/astronomy-photo/galaxies/m101/m101-galaxy.html

Click on the image to bring up the full resolution image and inspect the corners. Look very good to me except one of the corner.

This old medium format lens is impressive. There are not many old cheap medium format lenses with ED glass elements, they are too old for that. The never APO medium format lenses are very expensive and have electronic aperature and focus which can be complicated to use in an astrosetup.

/Lars

Utmarkt, tack for forkaringen. 

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  • 2 weeks later...

One more clear night and I could do more test of my new setup. This night I tested to autofocus the lens. First I used APT which I downloaded the latest Betaversion of. In the Beta version is a more advanced autofocus function implemented. I got it to work, but there are things that need more development. I installed N.I.N.A. which also have an autofocus function, it worked pretty good and I could setup the focus motor's backlash compensation correctly.

 

Some screendumps and explanation text of what I did:

http://www.astrofriend.eu/astronomy/projects/project-pentax645-300ed/01-pentax645-300ed.html

 

/Lars

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  • 2 weeks later...

Today I anlyzed my flats that I have taken with my Pentax 645 300 mm lens, they are takne at full aperture, f/4. As I expected the vignetting is very low, much lpwer compare to my Canon 300 mm L lens. That was one of the goals. Of course I want it to be a sharp lens too. It looks okay but at one corner the stars are a bit elongated, it must come partly because of a tilt of the camera house. The bayonette adapter doesn't fit very well and cause this.

This how the vignetting looks:
http://www.astrofriend.eu/astronomy/projects/project-different-lenses-vignetting/06-different-lenses-vignetting.html

/Lars

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A couples of days ago I fixed the tilt of the camera that I had. The tilt is caused of the bayonet of the adapter isn't tight enough. I thought about a lot of different solutions including a new 3D-printed adapter. But after a while I choose a very simple solution, a string and a spring that force the camera to be in correct angle and position.

Have a look at my photos from my Pentax 645 project:
http://www.astrofriend.eu/astronomy/projects/project-pentax645-300ed/04-pentax645-300ed.html

When the camera is out of focus the shape of the stars look very strange, but when in focus okay, all the way out to the corner. But must get the auto focus function to work better and calibrate the temperature compensation to get it perfect.

In the future I will 3D-print my own adapter and include some more funtions into it.

Lars

Edited by Astrofriend
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  • 1 month later...

It's the end of the astro season for us in Sweden, I maneged to take a last photo with my new setup with the Pentax 645 300 mm lens. That was good for me, I need motivation. I have struggled with this new system over 5 years, most problem with the Raspberry to get it to controll it.

This is the first astroimage with the new setup, are you curoius of how an 35 year old lens catch the stars ?

Very light polluted environment from my balcony, Bortle 9, but look at the shape of the stars at the corners of the full size photo, it's a full frame camera sensor.

http://www.astrofriend.eu/astronomy/astronomy-photo/open-clusters/m39/m39-open-cluster.html

Next thing to get to work is the dithering process, that will eliminate the hot pixels you see in the background. And then a suited battery and I can take it out to dark places, but that will not be until the next winter season.

I want to keep it below 25 kg included the HEQ5, lenses, computers and a battery that can handle 10+ hours.

/Lars

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  • 8 months later...

I did some analyzes of the astrophotos I have taken. There is a tilt of the sensor that I have to do something about.

 

Have a look:

http://www.astrofriend.eu/astronomy/projects/project-kstars-raspberrypi4/01-project-kstars-raspberrypi4.html

Not too bad for a 35 years old lens.

 

/Lars

Edited by Astrofriend
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  • 2 weeks later...

Here are some photos taken with the Pentax 645 300 mm ED lens, all taken at f/4, full opening. All images are not cropped, all the way out to the edge of the sensor and the sensor is full frame. Taken at Bortle Class 9 environment so no weak objects.

http://www.astrofriend.eu/astronomy/astronomy-photo/double-stars/big-dipper-stars/big-dipper-stars.html

I really like this lens.

When I look at the oversaturated stars, looks if something is in the way for the light beam, like an aperture. Have to look into the lens and inspect it carefully.

/Lars

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  • 2 weeks later...

Since last I have updated my Astroberry systems that control everything. Last update had an update of the auto focuser routine. It looks to do a much better job now (which wasn't bad earlier either).

I have documented what I found for you who find it interesting:
http://www.astrofriend.eu/astronomy/projects/project-pentax645-300ed/13-pentax645-300ed.html

It got a bit slower but I think I can tweak the parameters and get it faster. Just need a clear sky to test it.

/Lars

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  • 1 year later...

If one medium format 300 mm f/4 lens is good, then one more must be even better, or? I found a later version of the lens I already have and felt that I must buy it, not often they are for sale. It's a Pentax 645 FA* 300 mm ED IF f/4 lens. I haven't found all data about it but if I'm right it has 8 lens element insted of 5 that the older lens have. It's much heavier so some extra must there be inside. Here how it looks like:

http://www.astrofriend.eu/astronomy/projects/project-pentax645fa-300ed/01-pentax645fa-300ed.html

This will be a project for the future, maybe when I get a medium format camera that I can afford, then it needs the extra correction that this lens give.

/Lars

Edited by Astrofriend
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11 minutes ago, Astrofriend said:

If one medium format 300 mm f/4 lens is good, then one more must be even better, or? I found a later version of the lens I already have and felt that I must buy it, not often they are for sale. It's a Pentax 645 FA* 300 mm ED IF f/4 lens. I haven't found all data about it but if I'm right it has 8 lens element insted of 5 that the older lens have. It's much heavier so some extra must there be inside. Here how it looks like:

http://www.astrofriend.eu/astronomy/projects/project-pentax645fa-300ed/01-pentax645fa-300ed.html

This will be a project for the future, maybe when I get a medium format camera that I can afford, then it needs the extra correction that this lens give.

/Lars

This may be helpful 

 

https://www.pentaxforums.com/lensreviews/SMC-Pentax-FA-Star-645-300mm-F4-Lens.html

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  • 2 weeks later...
  • 2 weeks later...

The Pentax 645 300 mm f/4 ED lens is a heavy piece of metal and glass, it takes long time to adapt it to outdoor's temperature. I have with help of Siril done an analyze of the needed time to come in equilibrium:

http://www.astrofriend.eu/astronomy/projects/project-pentax645-300ed/15-pentax645-300ed.html

At least 1.5 hours for a delta temperature of 20 degrees Celsius.

/Lars

Edited by Astrofriend
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  • 1 month later...

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