Planewave updates

[jase (Jason)]

For those that didn't get to AIC this year (which includes me), it's been refreshing to hear about the latest developments across the Planewave instrument portfolio. I was quite impressed by their 3D printed baffle tubes further cutting the OTA weight.

Great to hear about their consultancy services for turn-key solutions. Bring it on. More remote imaging opportunities await.

Video released 20th December 2013
http://www.youtube.com/watch?v=NHi6qgdXE2s

[Bassnut (Fred)]

That's very cool, printed baffles,70mm image circle and especially 11" back focus. Becoming very attractive.

[Spookyer (Brett)]

Yeah, put me down for one of those mounts, and a 24" scope as well.

[gregbradley]

Having used a Planewave CDK17 now for several years I am very happy with Planewave. They also really back you up after you buy. For example I told Rick at the Gold Coast my scope tended to have a hot spot with the 16803 chip making flat fielding difficult and critical. He sent me one of these baffles for the primary mirror for free. He in the past has sent me free baffles for the corrector and he also offered to send me a replacement focuser once when I accidentally loosened something that allowed some packers that set the focuser to be square. I managed to handle it myself but that after sales service is awesome.

The baffles are very important to the CDK design as the only weakness of the system I have found has been excessive hot spot/vignetting on large chipped cameras.

The later and larger models also have side fans to remove the thermal boundary layer, I don't see that on the 14. But 14inch CDK that is light enough to cart around would be a magic instrument.

The Planewave focuser has always been one of the best around. It never slips, never is loose and is as strong as hell.

Planewave CDKs are also very easy to collimate and seem to keep collimation really well. Also the carbon fibre is great as focus tends to be the same each night if the ambient temp is similar.

I wonder about dew heaters though. I find the primary takes a few hours with the fans going to meet the ambient (its hotter than ambient and takes a while to cool). If the primary is more than about .8C above the ambient it tends to give softer images. .1 is max sharpness, 1C is a bit too much, 3 is way too much. So if you heat the mirror to above ambient I wonder if that results in less sharp images. So perhaps no free lunch for dew prevention there and possible consequences.

Greg.

[pvelez (Pete)]

Greg

if you don't mind, can you elaborate on the hot spot/vignetting issue you had with the CDK17?

I have the CDK12.5 and STX-16803 and find it difficult to flat field out my images - especially in green for some reason.

Jase,

I agree wholeheartedly re support from PW. They fixed up my focuser issues quick smart.

Pete

[gregbradley]

[QUOTE=pvelez;1045801]Greg

if you don't mind, can you elaborate on the hot spot/vignetting issue you had with the CDK17?

I have the CDK12.5 and STX-16803 and find it difficult to flat field out my images - especially in green for some reason.

Jase,

I agree wholeheartedly re support from PW. They fixed up my focuser issues quick smart.

Pete[/QUOT

Probably best if I post some examples. I'll dig one up. I tend to get an area in the centre that is brighter than the surrounds plus heavy vignetting. Flats don't often correct the vignetting. Baffles helped with the hot spot. I think the hot spot is less now since I fitted the primary mirror baffle PW sent me. Perhaps there is one available for the 12.5. My only concern with it is that it is relatively wide so its reducing the valuable aperture somewhat but I am unsure if its totally successful as I fitted it around the time I started using this small chipped SX camera so its no test. The SX camera shows almost no vignetting nor hot spot.

I find 6 flats, done with a white sheet over the aperture taken either at dusk or during the day with the roll off roof closed done at about 25,000 ADU. I then average combine these with no dark subtract. I then subtract a bias from the flat when callibrating the image. Your darks also are critical. If they are slightly off you will get surprisngly bad callibration results. So I make sure my darks are good, at the same imaging temp used and at least 6 subs for the darks, more is better. Take fresh flats everytime you move the camera. I also clean the filters and camera more often as cleanliness is far preferable to flats removing dust donuts and sometimes failing to do so.

As far as worse in green that may be due to light pollution or sky glow which is usually green. Light pollution seems to often be worst in the green channel.

I also remember a post by Rick that the CDK design and also other
RC type designs have conflicting variables. You can make it faster at the expense of more vignetting. You can reduce vignetting but at the expense of making the scope slower. So it comes down to what the market would prefer as a combination of qualities. It seems the 14 inch is a new compromise with long backfocus, less vignetting but slower F ratio. The new reducer sounds good with decent backfocus. The current backfocus is unworkable and not enough room for even an OAG.


Greg.

[pvelez (Pete)]

Thanks for the detailed response Greg

Your image looks similar to my uncalibrated images. Perhaps it's the big chip. I might look at the baffle option.

I process my images in PI and have been experimenting with different combine and dark/bias calibration. One thing that comes out clearly from the PI forum is the need to get the darks and bias right - as you have noted. The other point made by PI users is that flat fielding is tricky when there is "excessive" vignetting - this is why I was keen to hear about your experience with vignetting.

The 14 inch looks tempting - though I suspect my missus will consider such aperture fever more evidence of a mid-life crisis. But at least it's better than getting an earring, a blonde and a Harley!

I take your point on G being affected by LP. It's quite heavy duty here close to the city - another reason to head out of town and set up a remote observatory.

Pete

[rally]

Pete,

I agree - you cant have it all.
Ditch the Harley and the earring and just take the CDK14 and the Blonde.
Remaining well balanced is important !!

Sorry Jase for the intrusion

Rally