Which Flattener/Reducer?

[ashworthacca]

I have a Shywatcher Equinox 80ED and I'm looking for a Flattener/Reducer for it. I will initially be connecting my Canon DSLR but will be buying a Atik 314L CCD camera.

With that in mind I was looking at the Televue TRF 2008 but I'm looking for clarification that it will be ok for my requirements.

Any advice would be appreciated.

Thanks guys

[Bizibilder]

The Skywatcher flattener/reducer is especially made to match the ED80. It is primarily a flattener (to cover the chip of a DSLR easily) and hes 0.8 reduction in focal length as well. If you get that one you could also get the adapter: http://www.firstlightoptics.com/adaptors/flo-adapter-for-skywatcher-focal-reducers.html which is especially useful as it allows the F/R to be rotated easily, so you can align your camera and you can screw 2" filters onto it. (The F/R on its own screws directly onto the end of the ED80 focusser tube).

[michael.h.f.wilkinson]

Typically, flatteners (or flattener/reducers) for refractors are designed for a specific focal length, or a particular range, not one scope in particular. The TV TRF was designed for the range 400-600mm, so should be OK (probably, more than just OK , given their usual workmanship).

[ashworthacca]

Thanks both,

I didn't think the Skywatcher Flattener/Reducer was compatible with the Equinox but it does seem to be, it did work very well in my old Orion do very tempting.

[JacobvonChorus]

Televue stuff is always very high quality. I just ordered the TRF-2008 for my SW Equinox ED80 so if you wait long enough, I can post how well it performs. Could be a while though since I just ordered it.

Jacob

[ashworthacca]

Thanks Jacob, where did you get it from and how long to delivery?

[ashworthacca]

I've also read about spacing issues with CCD cameras, what issues will I come across using a F/R with a Atik 314L?

Thanks

[michael.h.f.wilkinson]

The spacing is important. The focal reducer/flattener is essentially a Petzval lens, which in true Petzval design scopes is at a fixed distance from the front objective lens. In those scopes, all the focuser needs to do is to put the CCD chip at the right distance from the Petzval lens. In the situation that the Petzval lens moves with the focuser (as with a focal reducer/flattener), you need to put the CCD at the right distance from the Petzval lens first, using spacers, and then move the combination to the correct spot to achieve correct focus.

[Zakalwe]

The Skywatcher flattener/reducer is especially made to match the ED80. It is primarily a flattener (to cover the chip of a DSLR easily) and hes 0.8 reduction in focal length as well. If you get that one you could also get the adapter: http://www.firstligh...l-reducers.html which is especially useful as it allows the F/R to be rotated easily, so you can align your camera and you can screw 2" filters onto it. (The F/R on its own screws directly onto the end of the ED80 focusser tube).

That FR is not suitable for the Equinox. The correct one is this: http://www.firstligh...-flattener.html

This works very well with the Equinox. This is a link to a single unprocessed sub exposure (click for full-size image), taken with a DSLR sized cooled CCD. There's a little bit of distortion in one corner which I think was down to slop in the standard Crayford focuser.

The TRF-2008 also works well and has the added benefit of increasing the focal speed of the scope to f5.

[ashworthacca]

The spacing is important. The focal reducer/flattener is essentially a Petzval lens, which in true Petzval design scopes is at a fixed distance from the front objective lens. In those scopes, all the focuser needs to do is to put the CCD chip at the right distance from the Petzval lens. In the situation that the Petzval lens moves with the focuser (as with a focal reducer/flattener), you need to put the CCD at the right distance from the Petzval lens first, using spacers, and then move the combination to the correct spot to achieve correct focus.

Hmmm, that sounds quite fiddly to do. How would I know which spacers to buy?

That FR is not suitable for the Equinox. The correct one is this: http://www.firstligh...-flattener.html

This works very well with the Equinox. This is a link to a single unprocessed sub exposure (click for full-size image), taken with a DSLR sized cooled CCD. There's a little bit of distortion in one corner which I think was down to slop in the standard Crayford focuser.

The TRF-2008 also works well and has the added benefit of increasing the focal speed of the scope to f5.

That single sub looks to pretty damn good all way to the corners, at £66 this flattener must surely be worth a punt. Thanks.

[michael.h.f.wilkinson]

Hmmm, that sounds quite fiddly to do. How would I know which spacers to buy?

Most focal reducers/flatteners specify which distance is required, usually with respect to the T2 thread of the camera adaptor. You can get spacing rings in all sorts of sizes (my TS flattener for the 80mm F/6 came with the correct one supplied).

[ashworthacca]

Most focal reducers/flatteners specify which distance is required, usually with respect to the T2 thread of the camera adaptor. You can get spacing rings in all sorts of sizes (my TS flattener for the 80mm F/6 came with the correct one supplied).

Thank you! That's put my mind more at ease.

Regards

[Zakalwe]

Hmmm, that sounds quite fiddly to do. How would I know which spacers to buy?

That single sub looks to pretty damn good all way to the corners, at £66 this flattener must surely be worth a punt. Thanks.

If you go for the Skywatcher one, then the spacing required is 55mm. On my CCD the sensor is 20mm behind the end of the mounting thread. 2 x 17mm spacers + the gap to the sensor gave me 54mm, which is near enough.

Bern at Modern Astronomy is a good source of spacers. FLO will probably have them too.

[ashworthacca]

If you go for the Skywatcher one, then the spacing required is 55mm. On my CCD the sensor is 20mm behind the end of the mounting thread. 2 x 17mm spacers + the gap to the sensor gave me 54mm, which is near enough.

Bern at Modern Astronomy is a good source of spacers. FLO will probably have them too.

The more I think about spacing the more I'm confused.

I'm assuming that the field flattener fits into the 2"focuser. Then the flattener then connects straight into the T Ring adapter on my Canon DSLR? Is the spacing ok or do I need to think abouit it using a DSLR?

I'll no doubt be back with loads of question when I eventually get the Atik 314L.

Thanks

[ashworthacca]

Ahhh, what about if I want to buy a LP filter. The EOS Clip filter I assume is no problem but what about other 2" filters....don't they alter the spacing, even on DSLR's?

[Zakalwe]

The more I think about spacing the more I'm confused.

I'm assuming that the field flattener fits into the 2"focuser. Then the flattener then connects straight into the T Ring adapter on my Canon DSLR? Is the spacing ok or do I need to think abouit it using a DSLR?

I'll no doubt be back with loads of question when I eventually get the Atik 314L.

Thanks

The Field Flattener has a 2" nosepiece that fits into the 2" focuser. The rear of the FF is threaded (C-Thread). The distance from the sensor on Canons to the front of the lens mount is 45mm. As long as your T ring adapter is 10mm (mine is) and has a C Thread (again, mine does) then the T Ring adapter just screws straight onto the FF.

When you get your CCD, it will be threaded with a C Thread. Just get the correct length of C Thread spacers to make up the correct distance.

HTH

[Zakalwe]

Ahhh, what about if I want to buy a LP filter. The EOS Clip filter I assume is no problem but what about other 2" filters....don't they alter the spacing, even on DSLR's?

They screw onto the front of the FF, which then goes into the focuser.

[ashworthacca]

The Field Flattener has a 2" nosepiece that fits into the 2" focuser. The rear of the FF is threaded (C-Thread). The distance from the sensor on Canons to the front of the lens mount is 45mm. As long as your T ring adapter is 10mm (mine is) and has a C Thread (again, mine does) then the T Ring adapter just screws straight onto the FF.

When you get your CCD, it will be threaded with a C Thread. Just get the correct length of C Thread spacers to make up the correct distance.

HTH

They screw onto the front of the FF, which then goes into the focuser.

Many, many thanks.....it took a little time but I think I get it.

All the best

[Zakalwe]

A picture paints a thousand words:

T Ring and FF

Assembled

For CCD

Assembled

[ashworthacca]

Pictures do tell the whole story, many many thanks.

All the best

[JacobvonChorus]

I ordered the FF/FR from my local astronomy shop, Focus Scientific. Delivery time is unknown but soon hopefully. Spacing is an issue and is something I plan on working out after I have all the equipment and know how much spacing I will need.

Jacov

[ashworthacca]

Jacov, I'm looking forward to seeing the results and hearing how you get on with it.

[Zakalwe]

Here's a single sub using the Televue TRF2008 focal reducer on my Equinox 80. The image has been de-bayerd in Neb 3 and a bit of levels applied.

I still have some eggy stars in the corners, and its probably slightly worse than the results that I got with the £70 Skywatcher field flattener (which shows just how good the SW item is, compared to the TV item which is 4 times the price).

I can probably tweak things by fiddling with the spacing but to be honest:

1) The weather has been so rubbish that I haven't taken a single DSO image since September

2) My CCD has a DSLR sized sensor so there's loads that I can crop without losing any of most targets. I can get the whole of M31 on there with room to spare.

3) The increase in focal speed from f6.25 to f5 is worth a little bit of eggy stars at the edge.

(Dunno why there's a weird grid over the image...I suspect that it's something to do with the Photobucket image compression routine)