Prime focus & Skywatcher 200P DOB

[peterbolson]

I want to try some prime focus photography using my DSLR & Sykwatcher 200P DOB on an equatorial platform, but of course the focuser doesn't travel far enough inwards to allow me to focus.

I don't want to move my primary mirror so I thought the easiest solution might be a low profile T-mount adaptor like this Clever Engineering - Low Profile M60 to T Mount Adapter

Unfortunately this only fits the 60mm diameter tube of the Skywatcher 2" rack & pinion focuser, not the tube of the Crayford focusser supplied with my scope which is about 54mm diam.

Does anyone know of a similar adaptor which would fit my focuser ?

Otherwise is the only solution to get a new low profile focuser, and would this actually work on my scope ?

Many thanks

Peter

[spaceboy]

Astro Engineering Max DSLR 2 inch camera adaptor (for Canon, Nikon & Pentax) You may still find you lack travel on the focuser so moving the mirror may be your only option. I had an EQP that tracked very well but locating the NCP is near impossible so there will always be a degree of error that will limit exposure times.

[peterbolson]

Thanks very much spaceboy. That looks interesting & at a very good price. I don't want to pay too much as I've no idea what I'll be able to achieve but it should be fun trying. I'll contact them to see what they think.

Peter

[peterbolson]

This looks like another possibility Accessories @ Modern Astronomy

The adaptor is the 3rd item down. Has anybody any experience of this ?

Peter

[spaceboy]

How old is your dob ? Newer scopes allow you to connect directly to the drawtube with no need for the 2" adapter. A 2" adapter is supplied all the same as some 2" EP's will not come to focus with out them. The adapter on MA would be pointless only offering mark free connection. There is also the question of it fitting older draw tubes. What is the diameter of you draw tube ??

[peterbolson]

Hi spaceboy. It's about a year old. I'm not sure of the names of the various parts of the focuser but the internal diameter of the silver coloured part is about 54mm and of the plastic T-thread adaptor which screws onto it is about 58mm diameter. I can't see how the T-thread adaptor on my camera could connect directly to this.

Just thought - does something like a FLO 2-inch T mount camera adapter slide straight into the T-thread adaptor on the draw tube, thus leaving out the 2" EP adaptor ?

[spaceboy]

Think we are going to need some pics. Your adapter doesn't sound right ?? It was internal dimensions we needed to know.

[peterbolson]

I've talked to the technical advisor at Scope n Skies & he says that individual Skywatcher dobsonians differ in the length of their tubes by several millimeters which is why some focus OK with a DSLR & some cannot be focussed at all without moving the position of the primary mirror. Sounds as if I'm one of the unlucky ones. He says there isn't any adaptor available which would help. He also said I might be able to help by altering the collimation because it could have have been supplied with screws that were very tight ( to help with transport ) but I can't honestly say that I really understood what he was telling me to do. I collimate it in the standard way & it seems OK.

Incidentally those are the interior dimensions.

[Carbon Brush]

Faced with this problem I would do the following...

Remove the focus assembly.

Point the scope at a distant horizon light. Or the moon.

Something you can't fail to find.

Hold the camera body over the gaping hole and using liveview view the image.

Move the camera back & forth to obtain focus.

Measure the focus point. Assistant useful here if you don't have 3 arms.

That gives you a camera body to scope tube measurement to work with.

Then look at the dimensions of DSLR adapters and focussers.

I have recently done something similar waving camera and eyepiece in mid air at back of my TAL200K.

It may be you need a low profile focusser.

David.

[spaceboy]

I would seriously consider getting a reticule EP and see how accurate you can track before you go into too much hassle or expense. Unless you are happy just using the DSLR for short exposures that is ??

[peterbolson]

Hi David - I've done that. That's why I thought the Clever Engineering mount would be the answer. I did actually buy one & it's very nicely made but unfortunately Neil Rees who makes it hadn't realised that the Skywatcher has a 2"Crayford mount with a smaller internal diameter than the 2" rack & pinion. He did say he might consider making one ( presumably if there was enough interest ) & if he did I'm sure that would be the answer. ( He did by the way give me a full refund - very nice man to deal with.)

Hi spaceboy - I'm really most interested in observing & only wanted to try my hand at short exposure DSLR ap without spending alot of money. I think the answer is probably to try piggybacking first

Anyway, many thanks for your help

[codeblue]

For those of you with the 200P Prime focus problem, I found a slight workaround, I could not get prime focus with my 200P + canon 1100D using the standard T-adaptor but If I attach a 2x Skywatcher barrow lens in front of the T-Adaptor it will allow me to just get in focus.