Planewave CDK's and other large aperture telescopes - does UK seeing support them?

[SimonIRE]

Hi All, 

I am new to SGL but active over on CN's (I have moved back to the UK after years working in the US). I am contemplating purchasing a Planewave CDK - probably the 12.5" (F8) but possibly the 14" (F6.7). I may use the x0.66 reducer if I get the 12.5" although its back focus requirements are incredibly tight and probably prevent using an OAG. I am interested to hear from any other imagers in the UK using a CDK or similar design large aperture scope. I have some doubts/uncertainty whether the seeing where I am (Kent - in a Bortle 5/6) will support this aperture. I

I would be grateful for opinions on this! Thanks.

Best, 

Simon

[tomato]

Hi Simon,

Welcome to SGL. I don't think there are many imagers with Planewave instruments based in the UK, but 8" and 10" RCs are quite popular and there a few Orion Optics ODK 14 owners on the forum.

I image small galaxies with Esprit 150 APOs,/ASI 178 cameras binned 2x2 so I'm at 0.94 arcsec/pixel, and that is frankly me being optimistic from my location in damp Shropshire.

Steve

[SimonIRE]

Thanks Steve - 

It would be great to hear from some of those RC and ODK owners too. 

Your experience resonates within mine alright!

 

Simon

Edited June 8, 2021 by SimonIRE

[vlaiv]

What is actually your concern about resolution?

If you can afford and mount large telescope - I'd say go for it regardless of the fact that you'll be seeing limited.

Just make sure you pick up sensible working resolution for your conditions. I'd say with such a large scope - target somewhere around 1.2-1.4"/px. That will be good sampling rate for most time. There will be few nights a year where it will be too high and few nights a year where it will be too low (provided your mount is good enough).

Even if you can't utilize resolution - you can utilize light gathering. Large aperture gathers more light and will offer faster imaging at given resolution.

[SimonIRE]

13 minutes ago, vlaiv said:

What is actually your concern about resolution?

If you can afford and mount large telescope - I'd say go for it regardless of the fact that you'll be seeing limited.

Just make sure you pick up sensible working resolution for your conditions. I'd say with such a large scope - target somewhere around 1.2-1.4"/px. That will be good sampling rate for most time. There will be few nights a year where it will be too high and few nights a year where it will be too low (provided your mount is good enough).

Even if you can't utilize resolution - you can utilize light gathering. Large aperture gathers more light and will offer faster imaging at given resolution.

 

My mount is good - its a 10 Micron 4000 HPSII and can pretty much carry anything. Thank you very much for this practical guidance. 

 

[DaveS]

As can be seen in my sig, I have an ODK12 which is natively sampling at 0.61 "/px, and is carried be a mount that can certainly support that plate scale, but a recent experiment with binning in software suggests that there is little to be gained in my location from going below 1.2"/px, except perhaps on the most exceptional nights.

Don't confuse seeing with transparency / darkness, as the visual guys frequently report the best / steadiest seeing on nights of mediocre transparency.

[iantaylor2uk]

The University of Central Lancashire has a Planewave 700 (i.e. a 700 mm diameter mirror , 27.5 inches) but not seen many images from it. 

Edited August 20, 2021 by iantaylor2uk
Correcting typo

[newbie alert]

Hi Simon, where abouts in Kent are you out if interest?

I'm aware that planewave use a dall kirkham design and not a richie chreitien..

Sure Peter Drew has his scopes  of the DK design from 10inch upwards..So maybe another option or pick his brains on bortle scale/ optical support

[Andrew_B]

6 hours ago, newbie alert said:

Hi Simon, where abouts in Kent are you out if interest?

I'm aware that planewave use a dall kirkham design and not a richie chreitien..

Sure Peter Drew has his scopes  of the DK design from 10inch upwards..So maybe another option or pick his brains on bortle scale/ optical support

Planewave do both RC and corrected Dall Kirkham scopes. I'm not sure who does standard DK designs other than Takahashi for their two smaller models of Mewlon.

[Mr Spock]

CFF do classical Cassegrains up to 400mm - also RCs. They look very nice too http://www.cfftelescopes.eu/products/reflector

Not many places you can get a planetary f20 these days.

[newbie alert]

1 hour ago, Andrew_B said:

Planewave do both RC and corrected Dall Kirkham scopes. I'm not sure who does standard DK designs other than Takahashi for their two smaller models of Mewlon.

I watched a TAIC and the owner of planewave was saying he decided to go with the dall kirkham design , maybe it was a certain model  of scope they was doing ...

[ollypenrice]

I'm in the South of France rather than the UK but I've spent considerable time imaging with both a TEC140 (0.9"PP) refractor and a 14 inch ODK (0.62"PP), sometimes on the same targets for comparison. I did an article in Astronomy Now on this comparison and also posted images for discussion on here. Many SGL members felt, as I did, that there was little to choose between the results though some felt the bigger scope had found a little more detail. I preferred the refractor stars, particularly on some targets where huge star spikes were intrusive. The ODK also suffered, on occasion, from flair from stars out of shot. However, to be fair to the ODK, the idea was to bin 2X2 on many occasions but the Starlight Xpress SXVH36 refused to co-operate, producing dark artifacts when binned. This robbed the big scope of much of its potential speed advantage.  

The 14 inch ODK project was set up in conjunction with a client. He, I think, would go for another 14 inch while I would stick with the large refractor. In short it comes down to personal preferences, probably more to do with peripheral factors like maintenance than the strict performance of the rig. It's worth noting, as well, that diminishing pixel sizes play towards shorter focal lengths or, at least, make shorter focal lengths viable for high resolution imaging.  In the UK with relatively few clear nights I would also factor in the time spent fettling reflectors versus the plug-and-play aspect of refractors.

Olly