250PX and DSLR

[warpi]

Hello,

I have just purchased the Sky-Watcher Skyliner 250PX. Now I would like to connect my DSLR (Sony Alpha 3000) with E-mount (NEX mount) to the 2" port of the 250PX telescope. I have measured that I get focus at 38mm between the port and the DSLR (which is exactly the same distance as when the focuser is at max-position. Now I have been searching for a stable adapter inbetween and have found the three following options.

1. $3.88: metal Macro Ultra-slim M42 to NEX Adapter For 17-31mm Extension Tube

http://www.ebay.com/itm/151561829249

2. $5.3: Fotga Black M42 Adapter Ring for Sony NEX E-mount NEX NEX3 NEX5n NEX5t A7 A6000

http://www.ebay.com/itm/351151703016

3. $81: True-2™ Sony Alpha Adapter

http://telescopeadapters.com/index.htm?true2_sony.htm

It seems that maybe option 3 will give less obstructions in the light path but option 1 really is so close to the CCD so that I cannot imagine that it will affect the light path either?

What would you choose?

[Tinker1947]

One of these while a bit expensive is a worth while investment....

http://www.firstlightoptics.com/adapters/baader-2-inch-click-lock-cl-extension-47mm.html

[warpi]

The "Baader 2" Click-Lock with 2" CL Extension 47mm" looks nice and seems convenient but it seems to add about 44mm in distance. I need a maximum distance of 38mm for the DSLR to focus in the 250PX.

I found that there is a difference between M42 (42x1mm pitch) and T-thread (42x0.75mm pitch)

http://en.wikipedia.org/wiki/T-mount

http://en.wikipedia.org/wiki/M42_lens_mount

Therefore, the “option 1” above will not fit the 2 inch to T-thread which comes with the 250PX without an M42 to T-mount adapter. Below I have linked to one adapter. This solution will give a light path of about 35mm.

http://www.ebay.com/itm/151100884975

Extra T-mount male to 2 inch (is not wanted to use the one supplied with the 250PX)

$18: http://www.ebay.com/itm/331321310845

M42 cap for protection of DSLR when not mounted

http://www.ebay.com/itm/161441268499

I also found a NEX to 49mm adapter and a 48mm to 2” adapter. This would give a light path of ~41mm and also with the possibility to add cheap 49mm UV-filter for protecting the DSLR. But this solution will be more expensive and I have read that a lot of people at stargazerslounge.com does not use any protection lenses for their DSLR because it would create light problems?

$20: 2” (telescope) to 48mm male

http://www.aliexpress.com/item/New-2-2-inch-to-M48-0-75-Adapter-For-Telescope-Eyepiece-Lens/945417346.html

$1.7: 48mm female to 49mm male

http://www.ebay.com/itm/371021051008

$25: 49mm female to 49mm female

http://www.ebay.com/itm/291386436842

$1.75: 49mm male to E-MOUNT (DSLR)

http://www.ebay.com/itm/191257328360

Then I have some questions

1. Will there be any difference of having 35mm or 41mm light path (because it is very close to the CCD sensor which is not so big in diameter itself)?

2. Will the M42 cap above fit the T-mount thread?

3. Is it ok to not have any protection glass of the DSLR when mounted in the 250PX?

[Tinker1947]

There is the option to replace the Focuser with a Moonlite, My 250PDS has one and doesn't need a extension to gain focus, as the Moonlite comes with a couple of spacers.....

http://www.firstlightoptics.com/moonlite-focusers/moonlite-cr-dual-rate-tri-knob-crayford-focuser-for-newtonians.html

http://www.firstlightoptics.com/moonlite-focusers/moonlite-installation-kit-for-newtonian-focusers.html

[warpi]

Tinker1947: Seems to be a nice piece of equipment for improving focus. But so far I have not had any problem with getting correct focus.

I have now ordered the cap (could probably be modified to fit T-module thread) and the T-module to M42 adapter linked above.

The 49mm solution and the True-2 would allow bigger diameter of the light path but I do not think it matters since the T-module diameter is only affecting so close to the sensor so there shall be no wanted photons comming there anyway (look at sketch below)

[warpi]

I found out that some of the dimensions were not correct so I refined the image as below. Still, there will be no limitation of the light in the case of using my DSLR with this telescope and the above purchased adapters.

[warpi]

Now I am searching for positive projection (using eyepiece and DSLR). I found this very descriptive picture which explains this and prime focus method.

1. $15.29 Fixed distance (~65mm) eyepiece projection accessory

http://www.aliexpress.com/item/Free-shipping-1-25-Variable-Projection-Camera-Adapter-Telescope-Eyepiece-Connection-Accessory/1063304385.html

2. $32.79 Variable distance (~106-135 mm) eyepiece projection accessory

http://www.ebay.com/itm/261484472413

Does anyone have experience of that a variable distance is needed in order to gain proper focus?

[warpi]

With some experimental testing (making eveything dark at home and just holding the camera at a certain distance from eyepiece) I found out that ~65mm could be on the edge of perfect considering no additional magnification. So starting at 106mm like option 2 above would not be ideal.

After some searching I found that there exist M42 extensiontubes very cheaply with steps of 7mm in distance, so now I ordered the below items for enabling positive protection of the DSLR as well.

Eyepiece holder

$8.99: http://www.ebay.com/itm/271710053398

Extension tubes giving the following possible extra distance configurations +0, +7, +14, +21, +28, +35, +42, +49mm (together with item above will make variable distance of ~65-114mm between telescope and dslr)

$5: http://www.ebay.com/itm/171470410295

[Tinker1947]

If you don't have a Coma Corrector the Baader MkIII kit comes with 3 different extensions, with your scope you will need a Coma Corrector.....

[warpi]

Coma corrector seems to cost a lot more money. My current idea of connecting the DSLR to the telescope is more like taking photos of what I have seen rather than making awesome photos. I hope this setup which I have now ordered will be sufficient to document what I have seen through my telescope.