'Upgrade' from 150P to 130P-DS...?

[Uranium235]

Yep the third hole is for another thumbscrew, you might have a spare one you can borrow from a barlow or extension tube.

The third screw will come into play when you start using a coma corrector, as you need a robust way of seating it in your focuser. Just using two screws leaves the whole imaging train open to rocking or movement whithin the drawtube. Its only a fraction of a mm we're talking about - but thats enough to upset one or two corners on a larger sensor. Having three thumbscrews 120degrees apart would eliminate any potential movement as the telescope points in different directions over the course of a session.

Your sensor is pretty much the same size as mine (22mm diagonal), so it may be a challenge for you to get perfect stars in all four corners. But this is only a £165 telescope we're talking about, so for that price one should expect to have to do a little work in order for it to approach the standard of an APO costing at least three times more.

I have three correctors for the 130, the badder MkII and MkIII, plus the Skywatcher corrector.

Out of the three, I prefer to use the Baader MkIII - it gives a better field than the Skywatcher, plus you have the option of T2 or M48 fittings. In M48 mode its gives a rather generous spacing distance of 57.5mm. The skywatcher is good, but that 0.9x  reduction makes the corners difficult to tame - though it might be worth a shot now Ive got a tiltable imaging train.

[Thalestris24]

Yep the third hole is for another thumbscrew, you might have a spare one you can borrow from a barlow or extension tube.

The third screw will come into play when you start using a coma corrector, as you need a robust way of seating it in your focuser. Just using two screws leaves the whole imaging train open to rocking or movement whithin the drawtube. Its only a fraction of a mm we're talking about - but thats enough to upset one or two corners on a larger sensor. Having three thumbscrews 120degrees apart would eliminate any potential movement as the telescope points in different directions over the course of a session.

Your sensor is pretty much the same size as mine (22mm diagonal), so it may be a challenge for you to get perfect stars in all four corners. But this is only a £165 telescope we're talking about, so for that price one should expect to have to do a little work in order for it to approach the standard of an APO costing at least three times more.

I have three correctors for the 130, the badder MkII and MkIII, plus the Skywatcher corrector.

Out of the three, I prefer to use the Baader MkIII - it gives a better field than the Skywatcher, plus you have the option of T2 or M48 fittings. In M48 mode its gives a rather generous spacing distance of 57.5mm. The skywatcher is good, but that 0.9x  reduction makes the corners difficult to tame - though it might be worth a shot now Ive got a tiltable imaging train.

Hi

I just fitted a mkiii mpcc to my 150pds. Not had an opportunity to even try it out yet but will bear in mind about the stability problem you mention. I wasn't aware of any problem before. I've gone for the 48mm fittings - seemed sensible with a big sensor (about 28mm diag).

Cheers

Louise

[Uranium235]

Thalestris24, on 06 May 2014 - 8:42 PM, said:Thalestris24, on 06 May 2014 - 8:42 PM, said:Thalestris24, on 06 May 2014 - 8:42 PM, said:

Hi

I just fitted a mkiii mpcc to my 150pds. Not had an opportunity to even try it out yet but will bear in mind about the stability problem you mention. I wasn't aware of any problem before. I've gone for the 48mm fittings - seemed sensible with a big sensor (about 28mm diag).

Cheers

Louise

The stability problem I mentioned affects all correctors used with the 130 (and has been known to afflict all sorts of telescope designs). The problem is with safety undercuts is that the thumbscrews or compression ring fail to fully engage the undercut (its part 2" barrel, part safety undercut), which often leads to the corrector "popping out" by as much as 0.5mm when a compession ring or screw slips into the undercut, thereby forcing the corrector upwards.

A way to check is to measure how far down the thumbscrews start (inside the 2" EP holder), then compare that to thte distance between the underside of the MPCC collar and the start of the safety undercut. You will find that the screws are either 0.5mm too high, or the undercut begins too far down (by 0.5mm).

Ive thought about sending a message to Baader in regard to this, but I doubt a redesign will come about on the say-so of one user. It would be less hassle to drill three new thumbscrew holes about 1 or 2mm further down the 2" ep holder, thereby ensuring the thumbscrews hit the undercut and nothing else.

Edit: If you dont fancy drilling your stock EP holder, a replacement can be gotten from TS with which you can perfect you modifications.

[Johnny666666]

I have three correctors for the 130, the badder MkII and MkIII, plus the Skywatcher corrector.

Out of the three, I prefer to use the Baader MkIII - it gives a better field than the Skywatcher, plus you have the option of T2 or M48 fittings. In M48 mode its gives a rather generous spacing distance of 57.5mm. The skywatcher is good, but that 0.9x  reduction makes the corners difficult to tame - though it might be worth a shot now Ive got a tiltable imaging train.

Very interesting point about the extra thumbscrews! I have often wondered about the effect on the image all this stacking of adaptors has - I have sometimes noticed on the 150P a small amount of play, depending what combination of adaptors I use. With time I will replace some combinations with purpose designed adaptors.

Sorry for the extra questions: You mentioned the Baader MKIII gives a 'better field' than the Skywatcher - do you mean quality of image or wider angle? I assume the 0.9x reduction of the SW CC gives a slightly wider field of view than the 130PDS would be capable of in prime focus?

Spacing distance: is this the distance from the sensor to the front of the adaptor? I'm not familiar with M48 mode - is this a fitting you use to connect to your DSLR or is it simply a large standardised thread system for assorted astronomical paraphernalia?

The m43 camera system has a sensor mounted much closer to the front of the camera than is usual (they have ditched the mirror) but unless I pay out £50 or £60 for a custom low profile T2 adaptor all adaptors I have seen move the m43 camera as far back as any other system - therefore I have a small issue with the 150P where the focussing tube is intruding into the tube assembly in order to attain focus.

[Thalestris24]

Hi

My MPCC seems pretty solid on the 150pds. There's only about 5mm of it poking out the drawtube and I don't want to undo everything to check the line-up with the thumbscrews. The mpcc has a wide undercut - I'd be surprised if it didn't mate with the thumbscrews. Maybe it makes a difference that I'm using M48 spacers i.e. not a t-ring? Or maybe there is a difference with the 130pds?

Anyway, here is a pic:

The locking ring isn't the mpcc one (which is not used in this configuration) - it belongs to the variable extension tube

When checking it the whole scope moves before anything else does! So hope it's ok.

Cheers

Louise

[Uranium235]

Thalestris24, on 07 May 2014 - 12:32 PM, said:

Hi

My MPCC seems pretty solid on the 150pds. There's only about 5mm of it poking out the drawtube and I don't want to undo everything to check the line-up with the thumbscrews. The mpcc has a wide undercut - I'd be surprised if it didn't mate with the thumbscrews. Maybe it makes a difference that I'm using M48 spacers i.e. not a t-ring? Or maybe there is a difference with the 130pds?

Anyway, here is a pic:

mympcc-2.jpg

The locking ring isn't the mpcc one (which is not used in this configuration) - it belongs to the variable extension tube

When checking it the whole scope moves before anything else does! So hope it's ok.

Cheers

Louise

If yours is set up for M48 (ie: with T2 thread removed from the corrector), then its likely that the corrector is mounted slightly further up the drawtube - meaning that the thumbscrews are fully engaging the undercut. I had my M48 extension tube arrive today, so like yours it will be 2" all the way to the camera

The proof of the pudding will be in the eating, so you wont know until you get it under the stars (whenever it decides to clear up!).

[Uranium235]

Sorry for the extra questions: You mentioned the Baader MKIII gives a 'better field' than the Skywatcher - do you mean quality of image or wider angle? I assume the 0.9x reduction of the SW CC gives a slightly wider field of view than the 130PDS would be capable of in prime focus?

Ive found the MkIII is more reliable in delivering round stars to the corners - but the skywatcher, while making the telescope faster - also makes it more difficult to get it right all the way to the corners (ie: you will end up cropping).

Spacing distance: is this the distance from the sensor to the front of the adaptor? I'm not familiar with M48 mode - is this a fitting you use to connect to your DSLR or is it simply a large standardised thread system for assorted astronomical paraphernalia?

The spacing distance for a DSLR is automatically achieved when you attach your cameras t-ring to the T2 thread on the corrector. If you want to use M48 mode, you will need to invest in some spacers and perhaps a low profile T-adaptor for your camera so you have room to play with.

[Uranium235]

All the bits are together now, and ive just completed the final job of shortening my allen keys enough to fit into the tight space - easier said than done as they took the teeth right off my hacksaw! So in the end I resorted to taking the file to it, which did the trick (with a bit of elbow grease).

So to summarise (left to right)

1) Stock 2" EP holder (M54 male thread)

2) TS tilt compensator (M48), into which the MPCC is mounted (via M48) - the whole assembly is then allen bolted to (1) via the back plate of the tilter (optical length 10.5mm).

3) Altair astro M48 10mm spacer

4) Brightstar 2" FW (21.5mm)

5) 383L+ mounted to FW via zero distance M48-T2 adaptor (383 chip distance is 17.5mm)

Total spacing: 59.5mm

Given that the usual spacing for my setup was 57mm (from the base of the M42 thread), working from the base of the M48 thread adds another 2.5mm - giving me an ideal distance of 59.5mm!   should be darn close.

[Thalestris24]

Nice mono image! Hope that all works ok - looks a pain to adjust!

Louise

[Johnny666666]

I'm lost...

[Thalestris24]

Very interesting point about the extra thumbscrews! I have often wondered about the effect on the image all this stacking of adaptors has - I have sometimes noticed on the 150P a small amount of play, depending what combination of adaptors I use. With time I will replace some combinations with purpose designed adaptors.

Sorry for the extra questions: You mentioned the Baader MKIII gives a 'better field' than the Skywatcher - do you mean quality of image or wider angle? I assume the 0.9x reduction of the SW CC gives a slightly wider field of view than the 130PDS would be capable of in prime focus?

Spacing distance: is this the distance from the sensor to the front of the adaptor? I'm not familiar with M48 mode - is this a fitting you use to connect to your DSLR or is it simply a large standardised thread system for assorted astronomical paraphernalia?

The m43 camera system has a sensor mounted much closer to the front of the camera than is usual (they have ditched the mirror) but unless I pay out £50 or £60 for a custom low profile T2 adaptor all adaptors I have seen move the m43 camera as far back as any other system - therefore I have a small issue with the 150P where the focussing tube is intruding into the tube assembly in order to attain focus.

Hi Johnny

Sorry you feel lost. The above pics just show various ways of coupling a coma corrector to a 2" focuser. Lots of people use T-connectors but the above use M48 thread connectors. In theory there should be less narrowing of the light path so reduced vignetting (I hope!). The distance beteen the focal plane of the cc and the camera sensor is quite critical. With a dslr you can connect directly to the back of the cc with an m48 ring (like a t-ring but with a larger diameter thread - http://www.firstlightoptics.com/coma-correctors/skywatcher-dslr-m48-ring-adapter.html).

Hth

Louise

[Uranium235]

Nice mono image! Hope that all works ok - looks a pain to adjust!

Louise

Hopefully it wont be too bad to adjust, and once its done I wont need to do it again. Perhaps a way of making access easier would be to use a filter drawer instead.

[Uranium235]

Johnny666666, on 07 May 2014 - 11:20 PM, said:

I'm lost...

Just go with the normal method of mounting you imaging train for now. If using a DSLR, its highly probable that its lightweight and therefore doenst require such a stiff mounting. Its when using a CCD that the robustness of the imaging train becomes an issue, my imaging train is 1.5kg+ so gravity was having an effect of the camera as it tracked the sky - hence the over-engineered solution... theres no kill like overkill

I think once you get a CCD, your mindset changes from "lets just get a photo, dont worry about the corners" - to "Ive paid for these pixels, I want to use every single one!".

[Uranium235]

Last night offered 15min of possibly the worst sky I have ever imaged under. It was so bad I switched to Ha in order to cut through the thickening cloud. This was with the tilter at default settings, with just a tiny bit of coma creeping in at the far bottom right corner. Its noisier than motorhead, plus theres no calibration and the cloud did an awful lot of damage - but not to the guiding as it was on a bright star, its surprising what a finderguider will put up with before throwing a benny.

Also, my dessicant needs recharging - had a bit of ice in there.