Altair Astro 6” Ritchey Chretien review

[kirkster501]

Hi John, I will weigh it and let you know.

I had a small fiddle with one of the screws at the back of the scope whilst looking through the cheshire and could see the reflctions slightly change so immediately put it back to what it was! Not touched the secondary yet. It looks pretty good TBH but the centre "spot " and the immediate adjacnet ring is not perfectly central. Very near to it but not perfect. So a little worj to do on it at some point!

Rgds, Steve

[johnrt]

Hi John, I will weigh it and let you know.

I had a small fiddle with one of the screws at the back of the scope whilst looking through the cheshire and could see the reflctions slightly change so immediately put it back to what it was! Not touched the secondary yet. It looks pretty good TBH but the centre "spot " and the immediate adjacnet ring is not perfectly central. Very near to it but not perfect. So a little worj to do on it at some point!

Rgds, Steve

I used this guide to help me get to grips with collimating mine 6" RC. It might be of help if you haven't already seen it.

http://www.astronomics.com/documents/astro%20tech/astro-tech%20at6rc%20collimation%20sheet.pdf

[johnrt]

A last update on my M82 image, this time with Ha added to the red to highlight the emission jets being blown out by the galaxy. I shot 18 x 15 minute Ha subs (remember I couldn't manage 5 minutes before I sorted the primary mirror out) and blended them to the red channel in Pixinsight.

This image takes the total imaging time up to 11 hours - 4.5 hours Ha and 6.5 hours LRGB.

[kirkster501]

Yep, seen that John thanks. In my case the Collimation seemed spot on but the optical axis was very slightly out. So I had that small "fiddle" and noticed that whilst it moved the optical axis itialso through out the collimation slightly as well. So I put it back to what it was (actually not quite as good as it was) to do some more reading up. Not as much info about regarding the RC as opposed to SCT which makes be slightly uneasy since not so much expertise to coem to tthw rescue! A lot of teh mechansisms seem to use the Takahashi Collimation scope I notice......... Yet the instruction manuals state to just use the Cheshire EP...

Rgds, Steve

[kirkster501]

Also John meant to say did you notice that the mount alignment is much more critical on such a long FL scope compared to the ED80? Very much more so! I was missing targets last night all the time.

I also don't have a FR as yet so need to image at the native F8 which means long exposures- slow compared to the ED80 which is my only other encouter with Astro Photography.

My reason to get the RC8 is to get bigger scale on galaxies and GC's.

Steve

Edited February 3, 2013 by kirkster501

[johnrt]

Also John meant to say did you notice that the mount alignment is much more critical on such a long FL scope compared to the ED80? Very much more so! I was missing targets last night all the time.

I also don't have a FR as yet so need to image at the native F8 which means long exposures- slow compared to the ED80 which is my only other encouter with Astro Photography.

My reason to get the RC8 is to get bigger scale on galaxies and GC's.

Steve

My HEQ5 handles the 6" & ST80 guidescope pretty well, I needed the longer counterweight bar to balance but it points accurately and tracks away at up to 15 minute exposures with just a polar align via the polar scope (no drift aligning here!!).

I strongly suggest you make sure you align the finder scope in daylight and you will be fine. I forgot once and what a waste of about 2 hours that was trying to even put Jupiter on the chip without a finder was a nightmare!!

[kirkster501]

I spent a little more time looking at my collimation today using a cheshire and a 1.25 centering gadget. I think my collimation is good enough. I have the dot bang in the middle and concentric circles. I think it is OK.

With collimation there is always a monkey on my back saying "tweak it a bit more, go on you might make it a bit better still" !!! I think sometimes you have to know when enough enough. This is not the space telescope after all..... Speaking of which how the heck do the collimate the HST ?!!!!

[r3i]

I strongly suggest you make sure you align the finder scope in daylight and you will be fine. I forgot once and what a waste of about 2 hours that was trying to even put Jupiter on the chip without a finder was a nightmare!!

If you're doing planetary imaging with a webcam, a flip mirror is a big help in getting the target onto the tiny webcam chip.

[kirkster501]

Sorry, flip-mirror? Not sure I know what you mean by one of those.....? I do knwo the misery of trying to get a planet onto a webcam sensor though - its a frustrating PITA. Only way I can do it, on a SCT, is to massively defocus so I have a huge airy disk and then hope to catch that disk at some point as I slew around since even if the planet is out of the field, the airy disk edge may pass though it.....

[johnrt]

I spent a little more time looking at my collimation today using a cheshire and a 1.25 centering gadget. I think my collimation is good enough. I have the dot bang in the middle and concentric circles. I think it is OK.

With collimation there is always a monkey on my back saying "tweak it a bit more, go on you might make it a bit better still" !!! I think sometimes you have to know when enough enough. This is not the space telescope after all..... Speaking of which how the heck do the collimate the HST ?!!!!

Yep, you could be there for hours, I get mine as close as possible, but I'm not going to get hung up about it!

[johnrt]

Uh, dunno where my image has gone from in my post above, but here it is again!

[kirkster501]

That's a stunning M82 John. I hope I am good enough to get something like that one day

[jjongmans]

I've got the carbon 10" version. Collimating can be challenging and the only good way is with a defocused startest. I also used a Howie Glatter with holographic attachment and sighttubes, but it that isn't enough to get it at 100%. The biggest design flaw is the connection between focuser and primary mirror; if you adjust the primary mirror, you'll introduce tilt in the focuser. So you'll need a collimation ring (TS) to disconnect the focuser from the primary, so they can be adjusted independently.

[jgs001]

Getting some good results from it John.. I got the GSO version from Teleskop Service in Germany... I had some fun fiddling with the collimation off the bat, as you say it took some getting used to just how fine the adjustments were, but I didn't have the other issues you've seen. I too use mine with an ST80 on an HEQ5. I don't have a reducer, so I'm running at f/9 with my SLR, and it seems to be working fine for me using 10 minute subs. I've also used it for lunar imaging, and that's worked nicely. Although I have to admit to not having looked through it.

[Gonzo]

I might have to move my birthday forward a few months....

[r3i]

Sorry, flip-mirror? Not sure I know what you mean by one of those.....? I do knwo the misery of trying to get a planet onto a webcam sensor though - its a frustrating PITA. Only way I can do it, on a SCT, is to massively defocus so I have a huge airy disk and then hope to catch that disk at some point as I slew around since even if the planet is out of the field, the airy disk edge may pass though it.....

Something like one of these: http://www.widescreen-centre.co.uk/Products/Meade_Flip_Mirror_1_25.html

They allow you to flip between the light going to the webcam and the light going to an eyepiece at 90 degrees.

They take a little bit of initial setup to get the eyepiece parfocal with the webcam and also to adjust the position of the flip mirror so that when the object is centred in the eyepiece it is centred on the webcam chip. But you can do most if not all of that setting up in daylight.

An eyepiece with an illuminated reticle is also handy to assist in getting the target bang in the centre of the eyepiece. If your eyepieces are reasonably parfocal with each other, you can start with a low powered one and progressively swap to higher powered ones to get on target.

[kirkster501]

Gee whiz Mike, yet more money !!! They will keep inventing these things! TBH I have parked planetary AP for the time being and sold the scope I used for that. I am DSO for the the immediate future when it comes to AP. I will get a C9.25 when I am ready for some planetary AP. Not to say i wont give it a whirl with my RC* of course

[kirkster501]

Getting some good results from it John.. I got the GSO version from Teleskop Service in Germany... I had some fun fiddling with the collimation off the bat, as you say it took some getting used to just how fine the adjustments were, but I didn't have the other issues you've seen. I too use mine with an ST80 on an HEQ5. I don't have a reducer, so I'm running at f/9 with my SLR, and it seems to be working fine for me using 10 minute subs. I've also used it for lunar imaging, and that's worked nicely. Although I have to admit to not having looked through it.

Do you guys find the ST80 guidescope is too short a FL in comparison to the main imaging RC scope? I thought for best results they should be nearer in FL than is possible with the ST80? I have a Celestron 80mm guide-scope (though don't use rings) now with a longer 600FL though have yet to use it.

[johnrt]

The ST80 will be fine - PHD is capable of sub pixel guiding so will handle it. You could even go shorter with a finder guider and guide the RC successfully.

[jgs001]

Not in the slightest... as John said, the ST80 works perfectly... As a very quick and basic approximation using sensor crop factors, the equivalent focal length compared to 35mm (st80 400mm, RC 1390mm), when using my qhy5v and 450d is approx... st80 3400mm and RC 2224mm, so I'm actually looking at a much smaller area of the sky with the st80 and guide cam than I am with the RC anyway.

I'm sure there's more to it than that, to do with pixel sizes etc... but I have to admit to not being fully au fait with that, and I'm used to comparing focal lengths to 35mm (full frame) to get an idea of approx FOV anyway.

[ollypenrice]

That M82 is a real stunner. It's great to know that an instrument capable of producing that (in the right hands!) need not cost a fortune. It's very, very impressive.

Olly

[swag72]

These images make me wish I was less of a big girls blouse and had the confidence to try this fandangled collimation thing!! You've got it all working very well together John, well done for persevering and also writing such a comprehensive review.

[kirkster501]

These images make me wish I was less of a big girls blouse and had the confidence to try this fandangled collimation thing!! You've got it all working very well together John, well done for persevering and also writing such a comprehensive review.

Fantastic job he has done eh? !!! I bought a RC8 as well since I want to join this club. Won't be easy and a long road ahead i am sure, especially with our weather!

Couple of things things I have had to deal with right away is:

1. Finding the target at the longer FL - is more difficult than using a ED80 and requires better mount alignment.

2. The image scale, upon finding the target, is HUGE compared to the ED80!!

[r3i]

Couple of things things I have had to deal with right away is:

1. Finding the target at the longer FL - is more difficult than using a ED80 and requires better mount alignment.

2. The image scale, upon finding the target, is HUGE compared to the ED80!!

1. I tend to 'star hop' to a target rather than try to 'goto' it straight away. I set my camera up in the Nebulosity 'frame and focus mode' with an exposure time of around a second, then using CdC I goto a relatively near bright star then centre and synch it. From there I'll hop to a nearer star and so on until I've got to the target - usually only takes 2 or 3 hops. If I'm still unsure about what I have in the FOV, I'll take a relatively short exposure (10-30 seconds) then compare the resultant star pattern to an image of the intended object from somewhere like Google Images.

2. Yes, you'll find quite a difference in the FOV size to your ED80. If you haven't already got it, I'd recommend downloading CCDCalc which will help you get a feel for how objects will (or won't) fit into your FOV.

[johnrt]

Thank you for the comments guys, you are making me blush!

Seriously though what would the equivalent 900mm focal length f/6 triplet refractor set you back?