I am loving this scope as an upgrade from the ED80 but I cant seem to get a flat field even using the flattener.
As per the manual it says 75mm but the manual shows different spots to measure the 75mm from.
I have it 75mm from the start of the male thread on the field flattener but still get a little curvature with the ASI1600 which is tiny compared to a full frame circle flat field is suppose to have.
Also I am max extention on the focuser..even have to unscrew the rotater thread out a little to give me a few more mm for focus.
Wondering how others have theres set up, any help appreciated.
Hi Tony,
I can't help you with the 120mm Esprit, but I do have the 150mm Esprit and can comment on that.
My set up is a Canon 600D with a cold finger, Skywatcher flattener and spacer that came with it. The focuser is extended to 6 on the scale when using this setup. I'm an Astrophotographer and have never had an eyepiece on it.
The field is dead flat over the whole DSLR sensor with no sign of curvature.
For me this is a lovely telescope that I use to photograph DSO's greater than 20', for DSO's less than 20', I switch to a Meade 12" F8 LX850.
My final comment is that the 150mm Esprit will be with me until they put me in a pine box, "the Meade" well ask me in six months, I have only had it for a couple of weeks and have not had a chance to take any serious shots yet, all the above run on an EQ8, which I'm very happy with.
Cheers Peter, yes that what I thought some where between 6-7 not 8.
I am going to do some more test tonight, I'm thinking I may have the wrong Flattener out of the box.
@ the OP: When you say "a little curvature", are you able to quantify that, or show us an image? I've got a "little" myself, as seen in the attached image. I'm ok with that amount (ok enough not to spend another boat-load on another custom adapter anyway).
I had some questions about the spacing as well, due to inconsistent information from Skywatcher. I posted a thread about it on cloudynights, where someone provided an excellent response, which can be found here.
Thanks for link guys, will try to work it out, my flattener looks different to that, I'm thinking the smooth adapter ring they have attached to the flattener is the same as my griped one?
Did some testing last night.
attached is 75mm from the flattener start of the male thread as per Manual.
it was pretty close but still not flat
I added a 5mm spacer to make it 80mm and it go worse.
So I am close at 75mm but I am right at the end of my back focus..even have to unscrew the focuser rotater to give me a few more mm to focus.?
Pics attached.
75mm spacing...its pretty close.
80mm spacing it gets worse.
75mm spacing top left corner
80mm spacing top left corner.
Adding a solid extension tube (4-5cm long) in front of the flattener (on the telescope side) would give you some room for a manoeuvre and you would not need to fully extend the focuser. Having the focuser fully extended is not ideal because it increases chances of a tilt due to focuser sagging.
Hi Tony,
I have added an uncropped picture taken with my 150mm Esprit, you should be expecting the same results with the 120. On mine the distance from the CCD chip to the face on the corrector "past the thread" is 96mm. In the past when I have been checking the back focus distance I have assembled the whole lot and then removed the corrector and used vernier calipers to physically measure the depth to the CCD (I usually place a small piece of kimwipe over the CCD chip so I don't scratch it). I do this every time now, because I once got caught out where I failed to take into account the T Ring on the Canon (extra 10mm), if you measure the depth this way then it has to be correct. If the measured back focus distance is correct, then it can only be one of three things.
1. The CCD chip is tilted.
2. The corrector is faulty.
3. You Telescope is misaligned (not very likely, but still in the mix)
See if your supplier will lend you a new corrector so that you can rule that out of the equation.
Just my thoughts on the subject.
Thanks guys, I think I am pretty close wtih spacing may be out a mm or so that I dont have the exact right spacers but having to use the full extention of the focus tube is a problem in itself....I have Tasco checking it out as it doesnt sound right. will keep you posted and thanks for the response.
Adding a solid extension tube (4-5cm long) in front of the flattener (on the telescope side) would give you some room for a manoeuvre and you would not need to fully extend the focuser. Having the focuser fully extended is not ideal because it increases chances of a tilt due to focuser sagging.
EXCELLENT advice re using a spacer tube instead of using the drawtube (why SW made it come to focus that far out is anyone's guess) - this leaves you the option of having drawtube travel still. Make the spacer shorter than required, so you can accommodate extra and intra-focal adjustment
Quick one Tony, did you remember to account for the 6.5mm back focus of the asi 1600?
Yes thanks Lee, I am getting closer with current test now but still not perfect, I probably dont have the perfect spacer, could be 1mm out either way, not overly concerned about that but am concerned that I can only just reach focus full extended.
Latest Update, Tasco want me to return the Flattener to make sure its the correct one and working properly, it could be the wrong flattener.
Posting tomorrow.
tony i was going to say a couple of days ago are you sure that is the correct flattener, but thought better of it
it looks suspiciously similar to the flattener used for skywatcher doublets for f7.5 and greater and not for their apo's
pat
tony i was going to say a couple of days ago are you sure that is the correct flattener, but thought better of it
it looks suspiciously similar to the flattener used for skywatcher doublets for f7.5 and greater and not for their apo's
pat
Time will tell they should have it tomorrow, hopefully will hear back from them early next week.
right on cue mate 
