Yes, you absolutely need a flattener with any refractor. One step further. If the flattener on the refractor only supports up to an APS size sensor and not full frame and you choose to use your D750. Set the camera up to shoot in APS mode. As a D850 owner myself I am pretty sure you can do that on the 750 as well.
Thanks. I'll set it in APS mode and take it.
Here is the finalized items I am going to buy.
1. iOptron CEM40. Most likely I'll buy direct from them.
2. William Optics GT81 81mm f/5.9 Apo Refractor with Soft Case - Gold # A-F81GTIVGD.
3. William Optics All New 0.8x Reducer / Adjustable Field Flattener 6AIII for GT71, GT81, Z81 & Z103 Telescopes - Space Gray # P-FLAT6AIII
4. ZWO ASI290MM-MINI 2.1 MP CMOS Monochrome Astronomy Camera with USB 2.0 # ASI290MM-MINI
5. QHY Mini Guide Scope (with mount) this is $129. I also see William Optics 50mm f/4 Guide Scope with 1.25" RotoLock. or William Optics 32mm f/3.75 UniGuide Scope with Slide-base or ZWO 30mm. Which is better?
6. I need to get some battery pack for my setup. Exploring that as well.
At some point I'll be buying ZWO ASI533MC Pro.
I'll be using my D750 in APS mode. I am going to explore using my spare laptop and use with NiNA or some software. I am still looking for some kind of steps what I should use first etc. If you happen to know any place that I can refer, would be great.
I really appreciate everyone helping me to get this setup. I am glad that I am part this is community. Thanks a lot.
Edited by vsn, 30 December 2020 - 07:45 PM.