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First Light (Sort of!) with the Pentax67 300mm


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I bought the medium format f4 Pentax off Ebay recently and from a Japanese supplier. It cost me £120 with charges and VAT so quite a good price really. Anyway, it's in very good condition and is a lovely piece of glass. I've mounted it on the EQ3 Pro, now with a qhy mini guide scope:

P67_eq3-Pro.jpg.409ffa583350c2f2fc3fd87f4f6d90d2.jpg

P67_front.jpg.5b6bf79494c7c4c3fa195db2d8757303.jpg

It weighed a couple of kilos with the adapter and camera. I initially fitted it to a fs 1100d and did some subs the other week but had problems with the flats not working properly and with red halos around the brighter stars. It turns out I think the halos are caused by the Astronomik cls ccd lp filter... Very annoying but I'm pleased with the lens itself. I've been doing battle with the subs I took - I'm well out of practice with taking and processing dslr pics! I always get terrible lp gradients. I've had Pixinsight for about 3 years... So I finally got around to trying it, mainly to use the gradient removal processes (ABE and DBE). Works quite well but didn't eliminate the gradients entirely :( . I'm impressed with PI's colour calibration. It's certainly a powerful piece of dedicated astro software.

Anyway, here are the subs I took the other week with an unmodded 1100d. Nothing very exciting in terms of targets - just stars, really. The first lot I tried with the FS 1100d were 60s but seemed to be underexposed for the targets though, as usual, transparency was poor. The subs below were all 90s but seemed a bit overexposed - exposed to the right, overall. I'm going to have to try taking 75s ones! Also, I need a lot of them... None of the stacks are very good - if only I got more imaging opportunities....

Some stars in Herc. 23x90s:

Herc_23x90sPixGmp50pc.thumb.jpg.c0c8854d0ec68ea15bc83b7f38e23f0a.jpg

 

In the region of LDN712, 7x90s:

LDN_712_7x90s_pixGmp50pc.thumb.jpg.ba44e0ae53f53de3f76925d8f0a9dc35.jpg

 

M71, 7x90s (too faint to make out!):

M71_auto_7x90sPixGmpSynth50pc.thumb.jpg.20a62b6082460b704f12d52a16a112bf.jpg

 

NGC6823, 6x90s:

NGC6823_6x90s_autoPixGmpSynth50pc.thumb.jpg.d9ff4dc404becb9094863766f7483936.jpg

 

NGC6802, 14x90s:

NGC6802_16bit_PixGmp50pc.thumb.jpg.9022bb6f3ce949117d0800f77987b43e.jpg

 

 All stacked in dss.

Louise

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Wow, what a chunk of silicon dioxide have YOU! Congrats. You know, you could get a Pentax body to shoot the pictures onto... (I have two. Love 'em. Not as well supported with software as Canon or Nikon, but well enough.)

Now you qualify for posting in the Pentax Forums Astrophotography group, too. Really great group of people, can't say enough good things about 'em. Come to the Pentax Dark Side. We have cookies.

(I couldn't decide between that and "Now strike down your Canon body and take your place at our side".)

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7 hours ago, rickwayne said:

Wow, what a chunk of silicon dioxide have YOU! Congrats. You know, you could get a Pentax body to shoot the pictures onto... (I have two. Love 'em. Not as well supported with software as Canon or Nikon, but well enough.)

Now you qualify for posting in the Pentax Forums Astrophotography group, too. Really great group of people, can't say enough good things about 'em. Come to the Pentax Dark Side. We have cookies.

(I couldn't decide between that and "Now strike down your Canon body and take your place at our side".)

Hi Rick

Thanks for your response :) Yeah the lens really deserves a medium format dslr or, better still, a full frame cooled astro cam, neither of which I can afford. APS-C will have to do! At the same time, at F4, it would be a great lens for EAA. I don't think there is much demand for long vintage medium format lenses as they are too heavy for the handheld market. But they seem great for astro!

Louise

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Try also to use a Filter, you then can expose longer and gather more data" photons " with a filter like CLS Filter.. 

Else, very nice results, and encouraging to make more of them..:thumbsup:

 

Cheers

 

Martin

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1 minute ago, artem said:

Try also to use a Filter, you then can expose longer and gather more data" photons " with a filter like CLS Filter.. 

Else, very nice results, and encouraging to make more of them..:thumbsup:

 

Cheers

 

Martin

Hi

Yeah I did use a cls-ccd but that's what caused the red halos around the brighter stars. I've since swapped back to my full spectrum 1100d with another cls ccd fitted. I read somewhere that the haloes problem is associated with certain older cls ccd filters. Hoping the second one might be better and will try again whenever I might get some clear skies....

Louise

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3 hours ago, Thalestris24 said:

Hi Rick

Thanks for your response :) Yeah the lens really deserves a medium format dslr or, better still, a full frame cooled astro cam, neither of which I can afford. APS-C will have to do! At the same time, at F4, it would be a great lens for EAA. I don't think there is much demand for long vintage medium format lenses as they are too heavy for the handheld market. But they seem great for astro!

Louise

I might try this SharpCap Ascom dslr possibility https://www.cloudynights.com/topic/657429-how-to-use-sharpcap-with-a-dslr/

:)

Louise

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On 26/04/2019 at 12:54, Thalestris24 said:

a cls-ccd but that's what caused the red halos around the brighter stars

Hi. Are you sure? I thought it was that the Pentax 300mm's chromatic aberration was in the red (whereas normally we're used to blue). It's easy to fix though. Just back off the focus a little until the red halo disappears; a Bhatinov won't work as it will leave the red out of focus.

HTH

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48 minutes ago, alacant said:

Hi. Are you sure? I thought it was that the Pentax 300mm's chromatic aberration was in the red (whereas normally we're used to blue). It's easy to fix though. Just back off the focus a little until the red halo disappears; a Bhatinov won't work as it will leave the red out of focus.

HTH

I'm not 100% sure - it was something I've read, but I've always had the problem with the full-spectrum 1100d regardless of scope or lens used. If I ever get some clear skies I'll try fiddling with the focus.

Louise

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