Sky Watcher 130PDS or ST80 or 104

[Nicola Hannah Butterfield]

For cheap wider field than my 200P, I can do 300mm on my Canon lenses.

[JamesF]

The colour correction on the ST80 isn't brilliant and the ST102 is pretty much the same assuming you meant that one so they're probably not great choices if you're planning to use a DSLR.

The 130PDS seems to have a lot of fans here (I think it may have its own thread for images) and I think it would outperform either of the other two, though perhaps you may get some coma with a DSLR?

James

[JamesF]

This is the thread I had in mind:

https://stargazerslounge.com/topic/210593-imaging-with-the-130pds/

James

[Spaced Out]

If you've got a mount capable of astrophotography with a 200p and you're used to using newts (collimation etc) then the 130 PDS seems a reasonable choice. Coma corrector will be required too for decent stars right to the edge, of course a CC could always come later tho. I liked my 130 PDS so much I bought two in the end !

I had an ST-80 as a guidescope but I didn't really rate it for photography. I have no experience of the ST-102.

Edited March 30, 2020 by Spaced Out

[Nicola Hannah Butterfield]

@JamesFand @Spaced Outthanks for your replies, mount isn;t the issue bar connecting with the comp. and yes @JamesFread alot of it, just wondered if the acro's might have worked in wider configuration

[JamesF]

Years back there was an SGL member who was on a tight budget and started imaging with something like a Canon 500D and ST102.  He did really pretty well, I thought, but he was always fighting with bloated stars and flaring in his images.

If you wanted to try an ST80 then you'd probably have little trouble moving it on later if you weren't happy with it as they're quite popular as guide scopes or finders for large dobs.  I'm keeping an eye out for one at the moment myself, in fact.  On the whole though, I think the 130PDS is just a better bet straight out of the gate.  An image with obvious coma around the edges of the frame can always be cropped down if a coma corrector isn't immediately feasible.  There's not a huge amount you can do if different parts of the spectrum aren't all in focus at the same time though.

James

[Aramcheck]

With the 130dps & DLSR the focus drawtube has to extend quite a way into the OTA, which shows up on images with bright stars.

[Erling G-P]

2 hours ago, Aramcheck said:

With the 130dps & DLSR the focus drawtube has to extend quite a way into the OTA, which shows up on images with bright stars.

Is it responsible for this extreme effect ?   Been yanking my hair out over the cause of it!

This is a 200PDS, but I have a 130PDS too, and see tendencies of the same kind, for example on the Pleiades

[Whistlin Bob]

5 hours ago, Erling G-P said:

7 hours ago, Aramcheck said:

With the 130dps & DLSR the focus drawtube has to extend quite a way into the OTA, which shows up on images with bright stars.

Is it responsible for this extreme effect ?   Been yanking my hair out over the cause of it!

I don't think so- the effect is usually to make stars in one corner appear a bit Pac Man. That effect looks more like reflections somewhere in your image train.

For the OP- I can't comment on the STs as I don't have one, but the 130pds is wonderful providing you get a CC (the Skywatcher one has been good for me and f4.5 is good to image at) and don't mind a bit of DIY on the drawtube for the issue described above. With those 2 issues fixed it's a giant killer of a scope.

[Spaced Out]

1 hour ago, Whistlin Bob said:

I don't think so- the effect is usually to make stars in one corner appear a bit Pac Man. That effect looks more like reflections somewhere in your image train.

For the OP- I can't comment on the STs as I don't have one, but the 130pds is wonderful providing you get a CC (the Skywatcher one has been good for me and f4.5 is good to image at) and don't mind a bit of DIY on the drawtube for the issue described above. With those 2 issues fixed it's a giant killer of a scope.

Yeah I had some minor 'pacman' stars before I cut down the focuser tube.

[gilesco]

You can do Astrophotography with the ST series, I do so with the 120. It is a cheap achromatic refractor, and I get a FOV of roughly 100' x 75' with an ASI1600 sensor.

You should get a field flattenner, and to avoid achromatic aberrations (which you won't get rid of 100%) you will need to re-focus for each and every filter change.

The newtonian seems like a better idea to avoid all this hassle.

If you do want to go the cheap path and get the ST then look for a generic field flattenner, I use the Stellamira on my ST120 (https://www.firstlightoptics.com/stellamira-telescopes/stellamira-2-field-flattener-with-m48-adapter.html)

 

[Aramcheck]

9 hours ago, Whistlin Bob said:

I don't think so- the effect is usually to make stars in one corner appear a bit Pac Man. That effect looks more like reflections somewhere in your image train.

Here's an image I took with the 200dps, where the focus tube doesn't extend as far into the OTA. You can see the effect in the magnified portion.
Thanks for the heads up on reflections.

Also - if you shorten the focus tube I presume that it may cause problems when using the scope visually, when you have to fit the extension tube between the eyepiece and the focus tube?

Apologies to the OP for hijacking thread!

Cheers
Ivor

[Erling G-P]

Ah, so it does actually look like it does when you look down the tube and see the focuser protruding.

Apologies to the OP also from me, but hopefully some of the info will be of use regarding the possible issue

[alacant]

21 hours ago, Aramcheck said:

focus drawtube

Hi. Probably best not to get too hung up on the protruding tube. It's a design fault which takes all of 20 minutes to fix. 

In answer to the OP. No contest for me. Of the three, the 130.

Cheers and stay safe.

[gilesco]

3 minutes ago, alacant said:

No contest for me

Go with the 130PDS... or hold the money and go for something in the future...

[TareqPhoto]

The thread title mentioned two ST series, 80 and 102, and all people around the world keep talking about the achromatic and CA issue, and i know that, but i asked the question many times and i feel like i couldn't get the right answer or there are so many different opinions and then i couldn't reach the final one.

What do you think if someone used a mono camera with filters and keep focusing for each filter? What if you have 2 ST scopes with two same exact camera and each one has different filter, so you imaging 2 scopes and cameras at the same time with different filters and each has been focused for that filter? Will that make any difference? imagine you have two or 3 same achromatic scopes and three same cameras and each carrying a filter let's say R G B, or narrowbanding Ha OIII SI, each are focused, will the result be very different than for example a triplet with one camera and rotated filters?

Newtonian is color-issue free, only needed a coma corrector, but a refractor also mostly needing a flattener, so we aren't stopping here about correcting the field, but about the colors issue, nice thread and topic as i want to see all possibilities and options.

[gilesco]

1 hour ago, TareqPhoto said:

The thread title mentioned two ST series, 80 and 102, and all people around the world keep talking about the achromatic and CA issue, and i know that, but i asked the question many times and i feel like i couldn't get the right answer or there are so many different opinions and then i couldn't reach the final one.

What do you think if someone used a mono camera with filters and keep focusing for each filter? What if you have 2 ST scopes with two same exact camera and each one has different filter, so you imaging 2 scopes and cameras at the same time with different filters and each has been focused for that filter? Will that make any difference? imagine you have two or 3 same achromatic scopes and three same cameras and each carrying a filter let's say R G B, or narrowbanding Ha OIII SI, each are focused, will the result be very different than for example a triplet with one camera and rotated filters?

Newtonian is color-issue free, only needed a coma corrector, but a refractor also mostly needing a flattener, so we aren't stopping here about correcting the field, but about the colors issue, nice thread and topic as i want to see all possibilities and options.

I do this (ST120), you can see some results on my website. I find it difficult to focus Blue in particular, the stars are always larger than in say the Red and Green wavelengths. It is partly because the focuser isn't particularly good on this scope, and the motorised focuser only pairs with a DC motor, not a stepper motor, you can get a replacement focuser for the ST120, but to be honest I am saving up for an apo and I'm not now going to continue the investment in the ST120, but I will still use it until I can afford an apo (and a stepper focuser etc...)

[JamesF]

5 hours ago, TareqPhoto said:

What do you think if someone used a mono camera with filters and keep focusing for each filter? What if you have 2 ST scopes with two same exact camera and each one has different filter, so you imaging 2 scopes and cameras at the same time with different filters and each has been focused for that filter? Will that make any difference? imagine you have two or 3 same achromatic scopes and three same cameras and each carrying a filter let's say R G B, or narrowbanding Ha OIII SI, each are focused, will the result be very different than for example a triplet with one camera and rotated filters?

There are a number of things that come to mind that may or may not be a problem depending on the circumstances.

As regards using RGB filters, the CA issue still applies.  It's not that "red" doesn't come to focus at the same position as "blue", for example.  There's a continuum because the point at which focus is good varies with wavelength.  Colour filters allow a range of wavelengths to pass and therefore the focus position will be different for light of the shortest wavelength that can pass through the filter when compared to the longest.

Using narrowband filters may be slightly more successful because they allow a far smaller range of frequencies to pass through and the variation in focus position will therefore be much smaller.

There is another issue to be considered however, which is what the change in focus position actually means in terms of the physical characteristics of the optics.  When we say the position of good focus moves, what we actually mean is that the focal length of the optics varies with the frequency of light passing through them.  In turn that means the image scale (arcseconds of sky per pixel) and the field of view change.  When it comes to align and stack the subs it's possible therefore that they may not actually match up without rescaling the subs.  Not all stacking applications can do this (I don't believe DSS can, for instance).

How much of an issue these are probably depends on a the combination of the OTA and camera.  In some configurations it may not be that much of a problem whilst with other kit it may be awful.

James

[R26 oldtimer]

Having just posted an image with the ST102, I can say this:

-Can I get good images with the ST102 or ST 80? YES, but with narrowband filters. Osc or mono with rgb filters won't cut it.

-Do I prefer the ST102 over my 80ed? Certainly not, even for narrowband, despite the ST being faster.

Should one try imaging with the ST102? Sure! Something is better than nothing, although I would try only narrowband or nebulocity with the stars removed with starnett.

If I don't have any other scope or no scope's at this focal length, should I go for the ST or the 130pds for imaging?  As they are similarly priced, definitely get the 130pds. With a coma corrector it is a proper imaging scope, and there is a pretty long thread to support it.

 

Edited April 2, 2020 by R26 oldtimer
Typo

[TareqPhoto]

Ok, this will support my plan more then about getting a Newtonian over achromatic refractor even if i will do narrowbanding, so CA isn't the only issue but other physical issues then.

I don't know if i asked about ED semi APO or doublet then i will get same similar answer then as someone said that ONLY TRUE APO TRIPLET can do the job, this will put it at $$$$ route as well.

Thank you very much