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Flatteners / Reducers for RC6


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I have done my fair share of searching around to find out the best setup for doing AP with a RC6 and getting there but very confused to what reducer or Flattener to use, or whether I really need one.
I know this sounds maybe something fundamental I should be able to work out myself but so far I have only used a flattener, which I understand why is required for AP, but I have never really understood why most RC6 users seem to use reducers. 
Also when you read the advertising for the RC6 it sort of hints that they produce a pretty flat FOV without any reducer or flattener. I cannot comment on what mine produces as not yet used it for AP.

So my setup is an IOptron RC6, Upgraded with a Baader Steeltrack focusser, filter-wheel and either my ZWO1600 or QHY268M camera.

So my questions are:

  • I know I do not need anything to take images but is there a need for a flattener or reducer to get a full flat field ?
  • Or does this really depend on chip size of the CCD ?
  • What advantage is there in using a reducer, I understand it can reduce the exposure times but surely unless the image is far bigger than the FOV produced by scope on camera chip why would I want to reduce the size and then have to crop the image more, surely that reduces the image resolution ?
  • If it turns out I will be better with one what are the recommendations for this setup easily obtained in UK ?

Steve

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5 minutes ago, teoria_del_big_bang said:

I know I do not need anything to take images but is there a need for a flattener or reducer to get a full flat field ?

Hi Steve,

I've had a StellaLyra RC6" for a couple of years and almost immediately upgraded the focus unit to a BDST and purchased an AstroEssentials reducer.

I was reasonably happy with the results but the star shapes were never that good. Just this week I have 'played' at improving the collimation using a star test and, with reducer fitted, got the best concentric rings patern I could - it wasn't perfect but I couldn't get it any better. I then went on a imaged M13 and was pretty happy with the results. On Thursday night I removed the reducer and imaged M13 again with better results- better focus and better star shapes across the image. I'm not saying I have a perfect collimation but for a £375 OTA I am more than happy with the result.

My reducer is staying out and I am going to enjoy 1370mm for a while.

Adrian

P.S. I did share the results - I guess you've seen this:

 

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P.S. I just fitted my Canon M6 MkII to the RC and I am hoping it really does stay clear enough for me to grab 60 mins on M13 again and grab some colour.

Fingers crossed!

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9 minutes ago, Adreneline said:

Hi Steve,

I've had a StellaLyra RC6" for a couple of years and almost immediately upgraded the focus unit to a BDST and purchased an AstroEssentials reducer.

I was reasonably happy with the results but the star shapes were never that good. Just this week I have 'played' at improving the collimation using a star test and, with reducer fitted, got the best concentric rings patern I could - it wasn't perfect but I couldn't get it any better. I then went on a imaged M13 and was pretty happy with the results. On Thursday night I removed the reducer and imaged M13 again with better results- better focus and better star shapes across the image. I'm not saying I have a perfect collimation but for a £375 OTA I am more than happy with the result.

My reducer is staying out and I am going to enjoy 1370mm for a while.

Adrian

P.S. I did share the results - I guess you've seen this:

 

Cheers for that Adrian, as yet had not seen that thread so thanks for the link , I am pretty convinced now to at least start out without any reducer or flattener. I had sort of decided that a while ago when I first started setting it all up but after doing some searches generally on various sites I just couldn't see many not using a reducer.

Steve

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You shouldn't need a reducer / flattener - the RCs have a pretty flat field. The only reason for using a reducer would be to alter the pixel scale on the camera or to increase the 'speed' of the set up. My RC8 is F8 and gives a pixel scale of about 0.48"/pixel. With the reducer this goes nearer to F6 and 0.74"/pixel.

For the RC6 the pixel scale is 0.57"/pixel with 3.8 micron pixels, but rather than add a reducer you can always bin 2x2 to give a good pixel scale and aid SNR.

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I have the StellaLyra RC6 and use a flattener, the TSRCFlat2, with my ASI533MC. 

50 minutes ago, Clarkey said:

You shouldn't need a reducer / flattener - the RCs have a pretty flat field.

This may be widely believed but is certainly not true with the RC6. I thought the same but had to crop my earlier APS-C shots without the flattener. FLO told me that the limit with the RC6 was a 4/3 sensor and so the ZWO1600 may be ok without flattening, but I've seen poor corner stars with the 1" 533 on AstroBin, hence why I leave it in place with mine. 

Also, I no longer BIN2 but image at BIN1 nowadays, as this seems to give better final images. 

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27 minutes ago, fireballxl5 said:

I have the StellaLyra RC6 and use a flattener, the TSRCFlat2, with my ASI533MC. 

This may be widely believed but is certainly not true with the RC6. I thought the same but had to crop my earlier APS-C shots without the flattener. FLO told me that the limit with the RC6 was a 4/3 sensor and so the ZWO1600 may be ok without flattening, but I've seen poor corner stars with the 1" 533 on AstroBin, hence why I leave it in place with mine. 

Also, I no longer BIN2 but image at BIN1 nowadays, as this seems to give better final images. 

So is THIS the flattener you use ?
That looks a good choice so may well be what I go for if I need it.
This is just a flattener not a reducer then which if I do have a problem then is what I would prefer.

I will get everything else together as it is and on a rare clear night at least get dome stars imaged to fully check collimation and also how flat the field is with both cameras and then go from there, if I need a flattener then I will fit one.

Steve

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Posted (edited)
16 minutes ago, teoria_del_big_bang said:

So is THIS the flattener you use ?

yes, this seems to be the same part. It is listed on the TS website here.

I expect that you will need one to use the whole field of view with your QHY268M.

Good luck and CS, Andy

PS my Border Terrier is from Skipton 🙂

Screenshot_20220514-093127_QuickPic.jpg.979cd35de07a53f93b08d444e06dbf17.jpg

 

Edited by fireballxl5
Added PS
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45 minutes ago, fireballxl5 said:

certainly not true with the RC6

Fair enough - I don't own one so it was my assumption. The 8" is flat for an APS-C size sensor so I thought the 6" would be too.

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17 minutes ago, fireballxl5 said:

Border Terrier is from Skipton

Took me a while to work out what on earth you were going on about.🤣

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23 minutes ago, fireballxl5 said:

PS my Border Terrier is from Skipton 🙂

Screenshot_20220514-093127_QuickPic.jpg.979cd35de07a53f93b08d444e06dbf17.jpg

 

Awww 🙂 

No idea why everyone says that when they see pics of dogs, maybe because they are generally so much nicer than many humans are to each other 🙂 

Steve 

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227069424_IMG-20220408-WA0005(2).jpg.76ef5b8ef724f8f28aa0d692f08a7865.jpg

Mine has shorter legs as my knees are bad and so can't walk too far but she still does well despite her short stature and 5 mile walks (albeit slowly and thats my fault 🙂 ) she does with ease so keeps me mobile which is good as I could easily end up not moving as much as I should as it does hurt getting up and down but not too bad once I am moving.

Steve

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6 hours ago, Clarkey said:

You shouldn't need a reducer / flattener - the RCs have a pretty flat field. The only reason for using a reducer would be to alter the pixel scale on the camera or to increase the 'speed' of the set up. My RC8 is F8 and gives a pixel scale of about 0.48"/pixel. With the reducer this goes nearer to F6 and 0.74"/pixel.

For the RC6 the pixel scale is 0.57"/pixel with 3.8 micron pixels, but rather than add a reducer you can always bin 2x2 to give a good pixel scale and aid SNR.

It doesn't speed things up it spreads it over more pixels.. can you really speed a photon up

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12 minutes ago, newbie alert said:

spreads it over more pixels

A reducer spreads over less pixels. In terms of optical 'speed', yes we could debate wording, but with everything else being equal more light will be gathered by the same number of pixels.

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18 hours ago, Clarkey said:

A reducer spreads over less pixels. In terms of optical 'speed', yes we could debate wording, but with everything else being equal more light will be gathered by the same number of pixels.

Yes you're quite right... Brain fart

I just don't like that speed terminology that's quite often used.." speeding up the optics"  you can't make a photon quicker, you made it fall shorter  

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I would imagine that RCs flatten the field natively, similar to how a flattener works for a refractor, up to a certain point. Once your sensor reaches a certain size that flattening effect may not be enough so you need to look at more expensive purchases. For a refractor you would look to a full frame flattener and with the RC you would look at an optional extra flattener.

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  • 4 weeks later...
Posted (edited)

Still not taken any images yet but getting there and a few more bits arrived today to get me to the finishing line.
I just thought I would ask a couple of questions to see what opinions are (if anyone has a similar setup and knows the answers)

Currently this is how I have the setup.
image.thumb.png.f7674048b5b4249c3921eef8687f06a0.png 

The flattener requires 109 mm back focus + I have 3mm thick filters so adding 1 mm for these.

So the first question is basically does anyone see any obvious flaws in this setup ?

And the second question is do I need that tilt plate in there as I understand the Baader Steeltrack has the ability to align the focusser in a similar way. I am thinking that the tilt plate is just somewhere to have a light leak unless I put some sort of tape around it where the gap appears.

TIA

Steve

Edited by teoria_del_big_bang
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The tilt plate has the advantage of being fixed, so any tilt will remain the same if you rotate the focuser at all. If you remove the tilt with the focuser you must leave it set at the same point. As you have a rotator it is probably not really an issue for you - but just something to remember if you take your set up to bits.

I have a similar set up with the flattener reducer on my RC8 and I have taped round the tilt adjuster as you have suggested.

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On 14/05/2022 at 09:26, fireballxl5 said:

yes, this seems to be the same part. It is listed on the TS website here.

I expect that you will need one to use the whole field of view with your QHY268M.

 

Hi, I have bought this flattener but struggling to get focus with it installed.
It looks like my focusser needs to go further in than its minimum position, it seems to be almost in focus but needs to go further,
I thought no problem and I could just remove one of the big diameter spacers attached between the focusser and the scope but if I do then the inner moving tube of the focusser hits the internals of the scope so at a minimum I have to have one of the 25 mm spacers + the tilt plate as I have below.

Can you post a picture of your setup that may help me understand my problem?

 

image.thumb.png.f7674048b5b4249c3921eef8687f06a0.png 

Steve

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