RC8 question - Forums

Topic starter

Sep 27, 2023

Hello

How much of a "must have" is a field flattener with this scope? I`d consider my collimation to be pretty close but i still have issues with stars in the very corners. I suppose it could be tilt as i`m still using the focuser that came with it. I`m using a QHY 168C so an APSC sized sensor.

Any advice most welcome…..

Pistachio_Enjoyer

Sep 27, 2023

Since your camera has an APS-C sized sensor, I would reccomend you get a FF. You are most likely experiencing field curvature.

Brian Boyle

Sep 27, 2023

Hi Alan

Yes. The RC field is curved, and becomes noticable more than a few mm off-axis.

I think an RC sold without a field flattener is the same as selling a Newt without a coma corrector.

Indeed, RCs are frequently marketed as - unlike a Newtonian - not needing correction. Since most RCs will be used for AP, this is misleading.

After stuggling to get good images with an ASI1600MM across my RC8's field, a good field flattener fixed the issue. Now I have a FF sensor, even that field flattener doesn't correct to the field edges - but that's my fault expecting too much from a 2inch flattener and focusser. And I find myself having to upgrade [happily] to an RC10 with 0.8x flattener/reducer built into a 3inch focusser.

RCs are wonderful telescopes for AP, so I am a little surprised that there isn't more out there on the market for flattening/reducing optics. I guess that's because RCs are not as popular [perception over collimation difficulties], and the flattening/reducing optics are expensive.

CS Brian

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Alan Hancox

Topic starter

Sep 27, 2023

Hello Brian

Thanks for your input. Can you recommend a flattener? I have a limited budget. Is there anything you`d recommend? I must admit i love the image scale it gives me and its surprisingly easy to guide my EQ6R Pro with an OAG.

Brian Boyle

Sep 27, 2023

Hi Alan

I use this one with my RC8

https://www.teleskop-express.de/shop/product_info.php/info/p4006_TS-Optics-2--corrector-for-GSO-Ritchey-Chrtiens-w-o-focal-reductionTS-Optics-RC-1-0x-Flattener-Image-Field-Corrector-for-Ritchey-Chretien---2--Connection.html

CS Brian

Sean Mc

Sep 27, 2023

Will a regular f/8 refractor flattener work with an RC?

Ian McIntyre

Sep 27, 2023

I have learned that a flattener is an absolute must have. I have a Starizona .65 reducer/flattener and even that leaves wonky stars in the corners.

Reg Pratt

Sep 28, 2023

I used to run dual RC8 with an IMX571. Even with a field flattener you will still have some curvature in the corners. I would consider it mild but noticeable. Wasn't a deal breaker for me at the time but it was the only thing about those scopes that I wasn't completely happy with.

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