#1  
Old 15-12-2020, 09:41 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
Pentax 645 300 mm ED f/4 lens

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/...645-300ed.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

Last edited by Astrofriend; 15-12-2020 at 09:59 AM.
Reply With Quote
  #2  
Old 15-12-2020, 12:53 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 17,149
I have one of these and used it extensively with a FLI Microline 16200.
It delivers a lovely wide view, easily covers a full frame sensor as it was designed to cover 60 x 45mm film and is easy to focus and it holds focus overnight.

https://pbase.com/gregbradley/image/170433412/large

https://pbase.com/gregbradley/image/169050011/large

Greg.
Reply With Quote
  #3  
Old 15-12-2020, 09:19 PM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
Hi Greg,
What fabulos photos you have taken with that lens. You must have many years of experience to make images like that. Do you live on the countryside with no disturbing street lights or is the narrowband filter that effective to reduce the light pollution ?

Great, thanks, I place your link on my page together with the Pentax lens so all understand why I bought this old lens.

/Lars
Reply With Quote
  #4  
Old 15-12-2020, 09:49 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 17,149
Thanks Lars.

These were all done at home in semi rural skies.

Narrowband filters are very effective in cutting out light pollution. These are Astrodon 5nm narrowband filters.

Greg.
Reply With Quote
  #5  
Old 20-12-2020, 09:47 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
Thanks Greg,
That give a hope to me. About one hour drive and I have a dark sky at the East to Southern direction. With that I mean dark relative where I live.

/Lars

Last edited by Astrofriend; 20-12-2020 at 10:01 AM.
Reply With Quote
  #6  
Old 11-02-2021, 09:07 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
With lot of cloudy nights I can spend many hours in front of the computer. The last days I have made two tube rings to the Pentax 300 mm ED lens.

Some photos of how I did it:
http://www.astrofriend.eu/3d-printin...m-bracket.html

As usual a lot of changes during the work. But good enough to do test, only the 180 teeth pulley left to design and 3D-print.

By the way, today I got my HEQ5 mount, it will much better with its lower weight when I'm on travel with my equipment.

/Lars
Reply With Quote
  #7  
Old 11-02-2021, 02:01 PM
AdamJL
Registered User

AdamJL is offline
 
Join Date: Sep 2010
Posts: 773
That's awesome, Lars

I have a Canon 300 f/2.8 IS and 500 f/4 IS that would be great for widefield shots if I could figure out how to mount them to my tripod. You've got me thinking, thanks
Reply With Quote
  #8  
Old 12-02-2021, 10:24 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
Hi Adam,
Here is more to it. Today I have made the pulley I will use to connect the lens to the motor focuser. I chosen the same 180 teeth that I have made to the Canon 300 mm lens.

Here it is:
http://www.astrofriend.eu/3d-printin...m-bracket.html

Now it's complete and ready for some test photos, but first I shall test my Canon lens more. Take it out to some dark place relative my home in the city.

ps.
Your Canon 500 mm f/4 lens must be very exiting to use for astrophotography.

/Lars
Reply With Quote
  #9  
Old 15-02-2021, 03:27 PM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
I have now done some test with the Canon 300 mm lens, very satisfaid with the result. Time to replace it with the Pentax 645 lens. When I did this I got one problem, the focus barrel on this lens runs backwards.

My project report:
http://www.astrofriend.eu/astronomy/...645-300ed.html

It wasn't a clear sky this night, have to wait until I get that and can do some test.

All these tests I do now are done from a very light polluted sky. But I can still see the shape of the stars, vigenneting etc to judge how the lens perform.

Lars
Reply With Quote
  #10  
Old 21-02-2021, 04:05 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
First light with the Pentax 645 300 mm ED f/4 lens.

http://www.astrofriend.eu/astronomy/...01-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
Reply With Quote
  #11  
Old 10-03-2021, 04:58 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
I got a clear night and some time to do test with this lens. My goal is to have it autofocus. The software I controlled it with, the APT has in its Betaversion got a more advanced autofocus function. I tested it and it works, but still a Beta version. Until it's finished I use N.I.N.A. which have a more devloped autofocus function, but this software is new to me and I need to learn how to use.

I took some screendumps and wrote some explanation text of what I did, page 5:

http://www.astrofriend.eu/astronomy/...645-300ed.html

/Lars
Reply With Quote
  #12  
Old 21-03-2021, 12:41 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
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/...ignetting.html

/Lars
Reply With Quote
  #13  
Old 27-03-2021, 07:21 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
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/...645-300ed.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

Last edited by Astrofriend; 27-03-2021 at 08:04 AM.
Reply With Quote
  #14  
Old 27-03-2021, 07:49 AM
AdamJL
Registered User

AdamJL is offline
 
Join Date: Sep 2010
Posts: 773
Awesome work, Lars!
Reply With Quote
  #15  
Old 28-03-2021, 11:49 PM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
Yes, I'm very satisfaid with this setup. I have some vignetting from the DSLR's mirror. If I later change to a mirrorless camera this problem will be gone.

I have thought about a Canon RP full frame mirrorless, but I'm not sure if that is the best mirrorless camera for astrophoto today. Anyone else who have some experience of full frame mirrorless cameras and astrophoto ?

Lars
Reply With Quote
  #16  
Old 30-03-2021, 02:45 PM
AdamJL
Registered User

AdamJL is offline
 
Join Date: Sep 2010
Posts: 773
Anything with a Sony sensor
That said, the Ra is no slouch, but I went through the process recently of thinking about mirrorless cameras. In the end, I decided on a dedicated astro camera.
Why? Because a Canon Ra isn't cheap. Neither are the great astro-cameras of course, but the Ra can't be cooled down. For that sort of money, I'd want a really excellent astro camera. That was the biggest thing that swayed me. Being able to cool the sensor not only means ultimate noise control, but more importantly, means darks can be taken at a different time to the lights. I no longer have to stay out in the field an extra hour or so (minimum) to collect darks. I can do it during the day whenever I want.

So just under two weeks ago, I changes from a Canon 5D IV to an ASI 2600MC, and have been very happy with it so far (there's definitely a learning curve to using an astro camera)

Sorry to throw that in, but give it a thought anyway
Reply With Quote
  #17  
Old 31-03-2021, 01:08 AM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
Hi Adam,
Yes, Sony sensor are today very good, but I think that Canon still have good sensors too, especially at high ISO setting and low readout noise. In Sweden we don't have that problem with the temperature, we can only observe in the winter and then it's somewhere -20 C to 0 C degrees.

Nowadays I don't take any darks or bias frames, solve the static pattern problem with dithering. It works fine with modern cameras with low static pattern and low ampglow.

I have seen used Canon RP at lowest for 700 Euro. Another very interesting mirror less camera is the Fujifilm 50R, it's a Sony medium format sensor in that camera. But then I have reached the cost of a monochrome ASI 6200mm full frame astro camera.

One big problem I have with my Canon DSLR camera is dust and dirt on the sensor. It's so deep down in the opening that it's very difficult to get it clean, I also get a lot of dry stain on the sensor after every clean. I have tried a lot of different cleaners and now I do my own from Isopropanol.

/Lars
Reply With Quote
  #18  
Old 31-03-2021, 10:40 AM
AdamJL
Registered User

AdamJL is offline
 
Join Date: Sep 2010
Posts: 773
Hi Lars

Well that's too cold for my bones!
Just try and keep the temperature constant between your lights and darks. A couple degrees difference is okay.

Don't forget also that if you do get a mirrorless, to get the best out of it, you should look to modifying it to increase Ha transmission. That could increase the budget a fair bit.

The ASI6200MM is an amazing camera! To be honest if I was buying a camera solely for astro work, then that is what I'd be using.

As for dust, have you tried these? I've used them on my cameras over the years with good success
https://photosol.com/products/sensor-swab-ultra/
Reply With Quote
  #19  
Old 28-04-2021, 08:50 PM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
Hi Adam,
The ASI6200 is a dream to have. But for the mpment the cost is too much.

I have test something like the dustremover you linked to, now I mix my own solotions. Isopropanol, dest water and maybe a little bit soup.

/Lars
Reply With Quote
  #20  
Old 30-04-2021, 11:56 PM
Astrofriend's Avatar
Astrofriend (Lars)
Registered User

Astrofriend is offline
 
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 339
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/...n-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
Reply With Quote
Reply

Bookmarks

Tags
medium format, pentax, vignetting

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 09:57 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
Advertisement
Limpet Controller
Advertisement
Testar
Advertisement
Bintel
Advertisement
NexDome Observatories
Advertisement
Astronomy and Electronics Centre
Advertisement