Focus questions

[FarAndBeyond]

Beginner here. So ive just purchased a used (but in good condition?) Skywatcher Explorer 200 (PDS I hope, and not the P?), I haven't got a chance to test it out or collimate it yet, received the telescope yesterday afternoon, but when looking thru the telescope out thru my window I have a hard time focusing on objects thats are lets say upp to 200 m away (houses obscuring longer distances than that).

I feel like the eyepiece needs to focus more "down" (I might be wrong though) into the tube in order to get better focus for the things I tried looking at, but the focus is already at the lowest, so it can´t go any lower.

So when focusing at objects more far away does the focus generally needs to come more out of the tube so to speak (further away from the secondary mirror)? Maybe I tried focusing at objects to near, can that be it?

Also when I used the huge 2" eyepiece (28mm) it was much worse than when I used a 1.25" eyepiece (25mm), so is there any difference between 2" and 1.25" even if they are almost at the same magnification?

Also, does collimation affect the focus of objects?

I´m a bit worried I will not be able to achieve focus on astronomical objects?

[steppenwolf]

Objects close to you require the focus tube to be racked outwards (i.e. the focus tube protrudes more from the optical tube). If you have a PDS version, you may need an extension tube to focus on nearby objects.

[bottletopburly]

If it has dual speed focuser it’s a PDS version, if it has original accessories then there should be an 1.25 extension and also a 2” extension too , post a picture of focuser and extension 

[westmarch]

I agree, your targets are too close. If you don’t have the extensions, wait for a gap in the clouds or take it to the nearest park. Good luck  

John

[fozzybear]

If you have PDS version you should have these one for 2" eyepieces and the other for 1.25" eyepieces to insert into the focuser

[FarAndBeyond]

Yes I have the dual focuser and the mentioned accessories, but what made me hesitate about it being a PDS is that the color scheme is different, on mine its a black body with a gold color print saying Skywatcher and a black dovetail plate. The most other 200pds ive seen has a white print in the back and also saying "200PDS" and a green dovetail plate. So I thought mine looked more like a 200P, except the dual focuser which I guess can be swapped? Also I could not find a tube length for the 200pds, but for 200p I found 920mm and thats what my scope is, if I measured correctly, and the 200pds suppose to be shorter (don´t know how much tough?)

 

Anyway, about the focus, I have had a chance to try to focus on objects further away and thats where it gets even worse, on close objects ive managed to get it better but on objects far away its just completely blurry, and the 2" eyepiece is even worse (28mm), I have also tried with 1.25" 14mm and 25mm.

So im basically out of focus so to speak, I cant focus more in either direction and its very blurry in all focus positions on objects far away? I understand when the focus needs to come out more you can use extensions, but what can one do when the opposite is needed?

Also does a reflector scope that needs collimation affect the focus heavily (especially on objects at longer distances)?

I also think I saw like horizontal lines among the blurriness all over the field of view when I looked at objects far away, but not so much (if at all) on objects near, what is producing these horizontal type of lines.

I can add that this scope came with an electric focuser installed, so its not possible to focus by hand, but I guess that has nothing to do with this problem.

[Ricochet]

It might help if you post a photo of your focuser set up in case you have it set up incorrectly. 

[fozzybear]

200pds = 1000mm focal lenght

[Skipper Billy]

The 200P-DS tube is 920mm long

DS stands for Dual Speed focuser - so if your tube is 920mm long and you have  a two speed focuser then you almost certainly have a 200P-DS and you will find it impossible to achieve focus visually until you add an extension tube.

 

[bottletopburly]

As above you have to use the extensions 

[FarAndBeyond]

Thanks, yes you are correct about the need for extensions, I tried with the 2" black metallic piece like in the picture above, and it became better on objects on longer distances.

But i´m a bit confused since it was said earlier that I need to have the focuser travel more inward for objects on longer distances, so since I had a bad focus yesterday when it was in its most inward position it shouldn't get better with an extension since that takes it more outwards not inwards? What have I misunderstood here?

Another question, you said that I need an extension for visual, so does that mean its not necessary for AP? If not is there any difference if using a DSLR or a CCD, webcam or whatever camera?

I have understood the P-DS is more suited for AP. But I read Skywatcher said something along the lines of "we have shorten the tube length to make it for suitable for AP", but it seems they have not shorten it then?

[Space Hopper]

I've always thought it ridiculous that scope manufactures (some of them) put scopes on the market

with focusers that will not even bring eyepieces to focus. Crazy.

My own Orion Optics scope was like this, and i ended up fitting a new focuser, one that did the job.

[JOC]

10 hours ago, Tubby Bear said:

've always thought it ridiculous that scope manufactures (some of them) put scopes on the market

with focusers that will not even bring eyepieces to focus. Crazy.

In fairness to the manufacturers I think telescopes are exciting things to receive.  Whilst there may be some examples where what you say is true (you said it happened to you) I expect many new users tear the packages open bolt them together and rush outside with stock eyepieces jammed into the obvious slot and try to use their equipment completely ignoring the deinstuctions.  I know I did, luckily I was fine, but SGL is full of people that aren't and that with a few pointers (almost in lieu of the instructions) do sort out an awful lot of folks who haven't read the the instructions in their excitement and do then find the equipment did function in its as bought state.

[CraigT82]

14 hours ago, FarAndBeyond said:

Thanks, yes you are correct about the need for extensions, I tried with the 2" black metallic piece like in the picture above, and it became better on objects on longer distances.

But i´m a bit confused since it was said earlier that I need to have the focuser travel more inward for objects on longer distances, so since I had a bad focus yesterday when it was in its most inward position it shouldn't get better with an extension since that takes it more outwards not inwards? What have I misunderstood here?

Another question, you said that I need an extension for visual, so does that mean its not necessary for AP? If not is there any difference if using a DSLR or a CCD, webcam or whatever camera?

I have understood the P-DS is more suited for AP. But I read Skywatcher said something along the lines of "we have shorten the tube length to make it for suitable for AP", but it seems they have not shorten it then?

I think there's some confusion in this thread!

Yes the PDS has a shortened tube length, this is to allow cameras to come to focus easily as cameras require more 'in focus'. This also means that to use eyepieces, which focus further out, you need to use the extension tubes supplied with the scope. 

When you attach a DSLR to the focus drawtube the camera sensor is buried deep in the body of the camera, hence you need to move the whole body of the camera further inwards so that the focus plane lands on the sensor, this is why cameras require more in focus.

Don't judge your scope based on what you can see through it terestrially, youll just het confused as its not designed for that. Get it out at night and point it to the moon and play around with the focus (be sure to use the extension tubes). It will make more sense then.

[FarAndBeyond]

Im still waiting for a clear night, there haven't been stargazing conditions, or any gazing conditions since I received my used HEQ5 Pro and 200P-DS, I guess thats typical when you receive new gear?  Yeah thats the exact reason I wanted the P-DS version and not the P since I planned to be able to use it for AP sometime in the future. The thing that the camera needs to focus more inwards than visual, is that only true for DSLR or for smaller CCD/CMOS cameras as well? Would you recommend buying a DSLR or a dedicated CCD/CMOS if one is not going to use the camera for other photography than AP, which of them generally gives better photos?

About manuals, I personally always read all manuals before I even touch in this case the mount and scope (its a good time to read manuals while waiting for the parcel), but unfortunately the manuals are often poorly written with very basic information, sometimes with a lot of spelling errors. For example the manual for HEQ5 seemed very basic in my opinion, and didn't made me on expert on the HEQ5 Pro mount, I also I claim that the manual even forgets to tell you some steps, for example about the settings circles that you should loosen the RA set screw again otherwise the RA setting circle can´t rotate with the RA axis.

[CraigT82]

1 hour ago, FarAndBeyond said:

The thing that the camera needs to focus more inwards than visual, is that only true for DSLR or for smaller CCD/CMOS cameras as well? Would you recommend buying a DSLR or a dedicated CCD/CMOS if one is not going to use the camera for other photography than AP

Well it varies really, dedicated astro cameras generally won't require as much in focus (also confusingly called 'back focus').  When you look at them online they will usually specify the back focus distance or the flange-sensor distance, which will tell you how far inside the body the sensor is. 

These dedicated cameras can be very expensive, with the cheaper ones having quite small sensors. One advantage of a DSLR is you get a great big sensor for not much money, however it may be noisier and less sensitive than a dedicated astro camera. 

One thing I will say is that whilst the choice of camera is important, the choice of processing software is even more important! Be sure to budget for software! 

There is a great book for beginners called 'Making Every Photon Count' by Steve Richards. I'd definitely recommend getting hold of a copy.

[FarAndBeyond]

22 hours ago, CraigT82 said:

Well it varies really, dedicated astro cameras generally won't require as much in focus (also confusingly called 'back focus').  When you look at them online they will usually specify the back focus distance or the flange-sensor distance, which will tell you how far inside the body the sensor is. 

These dedicated cameras can be very expensive, with the cheaper ones having quite small sensors. One advantage of a DSLR is you get a great big sensor for not much money, however it may be noisier and less sensitive than a dedicated astro camera. 

One thing I will say is that whilst the choice of camera is important, the choice of processing software is even more important! Be sure to budget for software! 

There is a great book for beginners called 'Making Every Photon Count' by Steve Richards. I'd definitely recommend getting hold of a copy.

Yes ive heard about that book, maybe I should read it.

Ive got a chance to try out the scope for the first time under the stars, but only very briefly since I was busy with other stuff. I have not collimated the scope yet, I had hoped that the collimation that the previous owner did stayed intact during the 3 day shipping route?

Anyway, inside the stars I could see the spider vanes and also a big black sphere in the middle of the star, which i´m pretty sure is the secondary mirror which is obstructing the view in the central portion of the object. I guess they are not suppose to be visible when looking at an object? So what makes them visible, is it an collimation issue?

Also, I briefly slapped on the focus mask and it only made the exact same focus mask pattern visible inside the star, not at all like how the instructions that ive seen online shows it should look, as I said it only transmitted the exact same focus mask pattern on top of the star.

[bottletopburly]

Yes you definitely need to read , Making every photon count, don’t mess with collimating until you have read how to do it and have the required tools to do it , 

collimating guide  here 

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/  

[Ricochet]

1 hour ago, FarAndBeyond said:

Yes ive heard about that book, maybe I should read it.

Ive got a chance to try out the scope for the first time under the stars, but only very briefly since I was busy with other stuff. I have not collimated the scope yet, I had hoped that the collimation that the previous owner did stayed intact during the 3 day shipping route?

Anyway, inside the stars I could see the spider vanes and also a big black sphere in the middle of the star, which i´m pretty sure is the secondary mirror which is obstructing the view in the central portion of the object. I guess they are not suppose to be visible when looking at an object? So what makes them visible, is it an collimation issue?

Also, I briefly slapped on the focus mask and it only made the exact same focus mask pattern visible inside the star, not at all like how the instructions that ive seen online shows it should look, as I said it only transmitted the exact same focus mask pattern on top of the star.

You are way out of focus. All stars (aside from the Sun with an appropriate solar filter) will be point sources through a telescope. Turn the focuser to make the stars smaller until they become points. If they start getting bigger again you've gone too far. If you reach the end of focuser travel before you find that point you will need to add or remove extension tubes as appropriate.

[JOC]

FWIW I own a 200P which sounds somewhat similar, I bet it's got a similar focusser - I don't have any problems getting my camera to focus just by plonking it into the normal extension with a T ring on the camera.

[CraigT82]

3 hours ago, FarAndBeyond said:

Ive got a chance to try out the scope for the first time under the stars, but only very briefly since I was busy with other stuff. I have not collimated the scope yet, I had hoped that the collimation that the previous owner did stayed intact during the 3 day shipping route?

Anyway, inside the stars I could see the spider vanes and also a big black sphere in the middle of the star, which i´m pretty sure is the secondary mirror which is obstructing the view in the central portion of the object. I guess they are not suppose to be visible when looking at an object? So what makes them visible, is it an collimation issue?

The collimation will most likely be off after it's delivery, you will need at the very least a cheshire/sight tube to collimate the scope again, this is something that needs doing regularly, it's not hard but it's essential really, especially if you want to image with it.

Having off collimation will not be the cause of the issue your having, that's down to focus - specifically it seems you are not able to reach focus on a star.

This issue comes up a lot on here and it's usually the same thing... either due to not using the extension tubes or using them incorrectly. 

Can you post a picture of your focuser with an eyepiece in it to help diagnose? 

 

[PaulR1]

4 hours ago, FarAndBeyond said:

...

Anyway, inside the stars I could see the spider vanes and also a big black sphere in the middle of the star, which i´m pretty sure is the secondary mirror which is obstructing the view in the central portion of the object. I guess they are not suppose to be visible when looking at an object? So what makes them visible, is it an collimation issue?

...

Like this ?

Below is one of mine using a 200 PDS from when I very first started . Its caused by being out of focus

[FarAndBeyond]

Yes mine looked almost exactly like the picture above with the spider vanes visible and the black spot in the middle, only difference was that the color of the star was blue on mine, and that I could see like a "bubbling" motion inside the star (maybe its atmospheric disturbances?).

And it looked like that when it was focused so that the star appeared very big, I could also focus so that the star became smaller and then the spider vanes etc. was not visible anymore, but then instead the stars looked almost only like simple streaks of light, not like the sphere that they looked like when they where bigger as in the photo above, although when the stars was focused so they were smaller they appeared brighter than when the stars was focused bigger. So im not totally sure how they suppose look through a telescope (not on photos)?

I know one thing and that is that they are not looking at all like the hobby astronomer photos I see online, but somebody said in another thread that stars are not looking the same when watched through a telescope as they do in Astro photos, is that correct? They seem to look much better on photos, maybe thats because of the long exposure times achievable with cameras, or something else that the camera does better than the eye?

On photos I see stars as bright spheres (sometimes with spikes), while when I watched them through the telescope they appeared either like small bright streaks of light or like dimmer spheres with the spider vanes and a black central portion visible, depending on the focus.

I own the Skywatcher Chesire collimator eyepiece, is that enough for collimation or would it be much easier with a laser collimator?

I can add that the eyepiece I used was the 28mm 2" eyepiece included with the 200PD-S. 

[CraigT82]

1 hour ago, FarAndBeyond said:

And it looked like that when it was focused so that the star appeared very big, I could also focus so that the star became smaller and then the spider vanes etc. was not visible anymore, but then instead the stars looked almost only like simple streaks of light, not like the sphere that they looked like when they where bigger as in the photo above, although when the stars was focused so they were smaller they appeared brighter than when the stars was focused bigger. So im not totally sure how they suppose look through a telescope (not on photos)?

Stars look like pinpricks of light when seen through a telescope in focus. Just like they appear with the naked eye, only much brighter. You will also see the 4 spikes coming off the brighter stars, these are called diffraction spikes.

If the star looks like anything other than a pin point of light then the telescope is not in focus (as in the image above).

You need to run the focuser in and out and find the point where the star appears smallest, that is the focus point. 

Images of stars still only show them as pinpoints of light, although the long exposures involved causes the stars to overexpose and 'bloat' outwards, making them appear much larger than they actually are. A correctly exposed image of a single star will show it to be a pinpoint of light. Amateur telescopes will never show stars to be anything other than pinpoints of light, due to the great distances involved. 

The Cheshire collimater you have will be fine, a laser is useful in the dark or if you can't reach the primary mirror collimation screws whilst looking through the Cheshire. 

[Stub Mandrel]

If you see stars like in the photo above you are not terribly far from being in focus.

Just turn the knob in the direction that makes them smaller.

In images brighter stars look bigger, I am still getting used to the fact that to you eye all stars look more or less the same size - a pinprick.