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Old 25-06-2017, 02:47 PM
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Question Lepus telecompressor, atik one 6.0 mono + oag on celestron 14 edgehd ota


I would greatly appreciate any assistance fellow imaging experts could provide on my imaging train setup. I am a complete ‘newbie’ in this area but do have an Engineering background… apologies for the long discussion post.

I recently purchased a C14 Edge HD OTA with the ATIK One 6.0 mono camera and OAG included.

I also purchased the LEPUS telecompressor and camera adapter as well to be used on my imaging train. However, when the Lepus telecompressor was ordered from Optec in Michigan by my local telescope supplier here in Sydney, the camera adapter was calculated to have a length of 75mm (approx.). The problem was that the OAG component had NOT be taken into consideration at that time. Thus, I received a camera adapter with the wrong length for OAG use. No big deal.

I emailed Jeff Dickerman at Optec to explain what I really needed was a new camera adapter etc. Jeff was very helpful in explaining how to recalculate it again for the correct length however I think he jumped the gun and thought I was using an external filter wheel (ATIK-EFW) when my ATIK 6.0 mono has a built-in filter wheel. So again, the calculations I was provided with where not correct.

The calculations performed are explained here:

I decided to precisely measure the exact adapter camera length required instead using my trusty Mitutoyo Vernier callipers to give me sub millimeter accuracy.

So here in lies my issues / questions:

1. The lepus telecompressor (x0.62 – 19414) (http://optecinc.com/astronomy/catalog/lepus/19414.htm) states that the overall back focus length should be 105 mm. Okay so if that is the case then the exact length of the camera adapter required should be 48 mm (+/- 0.5 mm).

This is based on the following calculations taken from the drawing provided below:
a. Distance from CCD to outer plate of ATIK CCD (optical back focus) - A
b. OAG ATIK One OAG only length – B
c. M42 Extension F -> M T-Thread + spacing between M42 Extension and Lepus Camera adapter – C
d. T-Thread Spacing Gap between Extension Adapter and Lepus Camera adapter - D
e. T-thread flange - E

Camera Adapter Length (mm) X = 105 – A – B – C – D - E
= 105 – 24.2 – 24 – 5 – 1 – 2.5
= 48.3 mm (+/- 0.5 mm)

The correct Lepus camera adapter part number should be #19392 – 48

Do the above calculations look correct?

Note: The ATIK tech specification states a back focus of 27 mm (+/- 0.5 mm) however, the ring attachment on the CCD has to be removed to allow the OAG to sit flush with CCD face (this length is 3.8 mm) according to the ATIK one Tech drawing (One_mech.pdf). The Length A measured above is thus 28 – 3.8 mm = 24.2 mm.

2. I have read that the Lepus camera adapter has to be pretty spot on accurate to the millimetre otherwise it could introduce vignetting issues etc. Is this really true? Has anyone else had slightly less or more than 105 mm (+/- 2mm) for example and how do you correct for it?

3. In order for me to ensure I hit the precise sweet spot of 105mm using my calculation above of 48 mm would it not be better for me to get a variable camera adapter as well and further reduce the main camera adapter fixed length so that I can some variability in the length due to spacer / gaps in the T-thread depths?

4. If I did go for one of Optec’s variable camera adapters (providing 25 to 42mm of back focus) then to ensure the total back focus length of 105 mm is retained the new Lepus fixed camera adapter length for ‘optimal’ variability would need to be:

Camera Adapter Length (mm) X = 48 – 25 – (42 – 25) * 0.5
= 14.5 mm (+/- 0.5 mm)
= 15 mm (rounded up)

So, this would give me the following range to work with when attached with the T-Thread Variable Camera Adapter:
X (min) = 15 + 25 = 40 mm
X (max) = 15 + 42 = 57 mm

Does this calculation look correct?

Seemingly according to Optec website, the minimum tube length for Edge HD is 17 mm! Which still works for my setup. I would need to order Lepus camera adapter part number #19392 – 17 instead. This will provide me 42 – 59 mm of range to work with.

5. Based on the OPTEC website specs on variable Camera Adapters for my Lepus telecompressor - 2100 2.1-inch dovetail receiver, I would need to order the #19390: VLC T-Thread camera adapter for NextGEN and Lepus telecompressors. Is this correct part number?

ULR: http://optecinc.com/astronomy/catalo...apter_rev1.pdf

Also noticed the Lepus Telecompressor came with a black spacer ring. But I have been told this is not required to be used in the C14 Edge-HD. Is this correct or not as I could not find much information on it's use?

Thanks for your time! Greatly appreciated.

Clear Skies!
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atik one 6.0, c14 edge hd, lepus telecompressor

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