[Postumus]

Greeting fellow K3 Pentaxians

I have an unusual question
I am using my K3 on a refractor telescope (80mm F7.5 or 600mm FL)
I have just bought a field flattener and I need to space it 55mm from the K3 CCD (I have a set of M42 spacer rings)
So I am trying to work out the distance in mm from the K3 sensor to the front face of the K mount
I suspect this distance is the same for all Pentax DSLR bodies otherwise Pentax lenses would not be universal
I have searched through the K3 manual without any luck, and don't want to damage the CCD by measuring it myself

Does anyone know what this distance is or can guide me to a place where I can find out
Many thanks

[photoptimist]

It's 45.46 mm.

Good luck and we hope to see your shots soon!

P.S. This table (Flange focal distance - Wikipedia) gives these distances for a great many cameras systems.

[Paul the Sunman]

45.46 mm for all K-mount cameras.

[Postumus]

hey fellow Pentaxians

THANK YOU so much

I promise to post some images once I solve all technical problems
- proper polar alignment
- See if EQ mount still tracks properly
- set up guide scope
- buy ST4 guide CCD
- buy IR/UV cut filter
and the list goes on but we all need a challenge
Clear Skies as astro-nuts would say

Attached Images

 

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Last edited by Postumus; 11-13-2020 at 07:31 PM.

[Unregistered User 8]

I promise to post some images once I solve all technical problem

Looking forward to seeing them..................

[DWS1]

I'm excited to see those images.

[PJ1]

Like they said - 45.46mm. But I only jumped in to say that is a BEAST of a telescope. I look forward to seeing your images.

[Mooncatt]

Good luck and, most importantly, have fun with it!

Meanwhile, I'll stick my limitations of no time and Astrotracer.

[DeadJohn]

...I have just bought a field flattener and I need to space it 55mm from the K3 CCD...

Does the field flattener have t-threads? 55mm happens to be the standard t-mount distance. An off-the-shelf t-ring for k-mount should give you that distance to the sensor, assuming that the flattener has those threads.

[Postumus]

Does the field flattener have t-threads? 55mm happens to be the standard t-mount distance. An off-the-shelf t-ring for k-mount should give you that distance to the sensor, assuming that the flattener has those threads.

I have a set of T2/M42 extension rings coming. At 55mm vs 45.46 +-1mm just a 10mm ring would do
And as a backup I do have standard Pentax extension tubes. I'm pretty sure there would be one with a 10mm depths

Like they said - 45.46mm. But I only jumped in to say that is a BEAST of a telescope. I look forward to seeing your images.

Its still some time away. I guess in photographic terms its just a 600mm ED F7.5 lens.
The main thing is going to be polar alignment. Up north you have Polaris to guide you
Here down south we only have Sigma Octans, a 4/5th magnitude star not even visible from light polluted city skies

Anyhow I just want to thank you all for your answers and encouragements

[Postumus]

Here is a single image of my country skies
Pentax K3, Pentax 14mm F2.8, no tracking or stacking
At ISO 400, 25 seconds, Levels boost in PS
A few elongated star images on the upper right
Not sure if its my lens or I should drop it down one step
It doesn't seem to happen with the Samyang 14mm
nor the Canon equivalent
Image taken June 2020
I boosted the levels slightly too much as evidenced
by the red wavy patterns towards the horizon.
But this image was processed for FB where quality is poor anyway
Not your exacting pixel peeping eyes!

[pcrichmond]

Greetings and looking forward to seeing some shots from your scope.
I found the standard T to K adapter is 10mm for the 55mm distance mentioned by DeadJohn.
Seems to work fine this way on a 102/f6.5 (660 fl) scope and .8x reducer flattener making it a 528 fl @ f5.2.
I have found that doing prime focus without the reducer, I do need to add approximately another 60mm of extension to allow enough in travel on the focusing tube to achieve infinity focus.
Have fun and enjoy those starry nights.

[savcom]

As someone who is just starting in astrophotography, I am very interested in this - thank you very much for the info. Up till now I have been using just my standard DA 18-135 and DA 55-300 zooms both with an Astrotracer and on a tracker mount and I'm looking to get my first 'proper' scope in the next few weeks.