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Achieving focus with skywatcher star discovery 150p and dslr


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You probably need to use a barlow lens, the 150PDS is designed to reach prime focus with a DSLR, the 150P is not.

 

Other options are to modify the focuser, move the mirror up the tube or use a camera that can get its sensor closer to the focuser.

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20 minutes ago, D4N said:

You probably need to use a barlow lens, the 150PDS is designed to reach prime focus with a DSLR, the 150P is not.

 

Other options are to modify the focuser, move the mirror up the tube or use a camera that can get its sensor closer to the focuser.

I'm very nervous about voiding warranties etc so i'll go with the barlow :). Something that's never been made clear to me is whether or not i use, say, a 25mm eyepiece at the same time as a barlow or if you can only use them separately. Would you be able to shed some light on that for me? 

thanks

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Start with moving the primary up the tube with the collimation screws. You have to be careful that the collimation screws still have enough travel for collimation. This shouldn't void the warranty.

Another idea is that a coma corrector may help. (You need one anyway.) For my 150pds I found that the Baader coma corrector changes the focus in the right direction, I hope a 150p owner can confirm this to be the same.

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3 minutes ago, Bprezzle said:

I'm very nervous about voiding warranties etc so i'll go with the barlow :). Something that's never been made clear to me is whether or not i use, say, a 25mm eyepiece at the same time as a barlow or if you can only use them separately. Would you be able to shed some light on that for me? 

thanks

For visual you can use the barlow with the eyepiece, it will increase its magnification.  The barlow cannot be used on its own.

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The Baader takes it just over 1 cm further out. Maybe this is just enough. I've also read somewhere that a persons sw scope was shipped with the main mirror at the bottom position. If this is the case here as well, using the collimation screws to move the mirror up the tube may be a possible solution. Worth investigating, I think.

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A barlow will generally cause the focal plane to be moved outwards and so it should reach to the DSLR sensor, but the focal length is doubled and the exposure time has to be increased or the number of exposures. More relevant is that being longer any movement of the tube is amplified, so you lose more of the exposures through them being insufficent quality.

So a barlow will move things but it introduces other problems.

The real solution is to move the mirror up the tube by 20-25mm then recollimate.

The other if there is a suitable item is a low profile focuser to replace the existing one, but not sure if they exist and the ywill cost money, everything costs money unfortunately.

If you move the mirror then you could also need a short extension tube, as when moved it means that the use of an eyepiece may not be possible as the focal plane is then too far out for an eyepiece.

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13 minutes ago, wimvb said:

Start with moving the primary up the tube with the collimation screws. You have to be careful that the collimation screws still have enough travel for collimation. This shouldn't void the warranty.

Another idea is that a coma corrector may help. (You need one anyway.) For my 150pds I found that the Baader coma corrector changes the focus in the right direction, I hope a 150p owner can confirm this to be the same.

The Star Discovery 150 does not have any collimating screws so you can't move the primary. The focuser is also simpler, just 1.25" eyepieces, the coma corrector won't fit.

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Just found out that this scope is the beginners version of the Explorer 150P. Just 1.25" and no collimation. Great for visual, but just not intended for astrophotography.

My advice: don't invest too much into this scope. Use it while you save up for either the 130pds or 150pds on an eq mount.

Good luck

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There is a member using their stardiscovery for astrophotography to great effect. If you dro not want to make any alterations to the telescope then use your dslr and lens directly on the mount using the l bracket that came in the kit (take the telescope off). A 135mm lens can create stunning images, I'll add a link in a bit.

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If using just your camera one of these will be useful, a red dot finder that fits in a camera flash hot shoe so you can still do your star alignment. camera red dot finder  The No EQ challenge thread where members are pushing their AltAz mounts to the max of the mount's capability. link here

An example of a recent image taken using the stardiscovery mount with a modded dslr and a 135mm prime camera lens, vintage prime lens can be picked up on ebay for £30-40, use what you have with your DSLR to get started only certain targets benefit from a modded camera so plenty to chose from. link here

 

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Right chaps. I've done a lot of thinking and i think it's best for me to go with a sky watcher 150PDS. I think the main reason for wanting the goto was me being lazy (your average 17 year old) and it would be much more convenient to banish field rotation issues associated with an alt-az. Thanks for all your advice everyone, it's all taken on board :)

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I'm sure that if you ask that question to your (our?) favourite scope supplier, they will be willing to advise you and supply you with the correct adaptor. This part of ap always reminds me of plumbing, for some reason.

Good luck

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1 hour ago, wimvb said:

I'm sure that if you ask that question to your (our?) favourite scope supplier, they will be willing to advise you and supply you with the correct adaptor. This part of ap always reminds me of plumbing, for some reason.

Good luck

Funny you should say that, for my 150p modifications I used plumbing pipe bits, and I'm a plumber :) 

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