Had an opportunity to borrow an AP160 scope for a little while and decided to do some side by side testing with the SW150 Esprit I have on hand. I've read in the past where a few folks were interested in such a test. The visual part of this test will come later. Hopefully by the end of the month. I am a photographer and have devoted all of my time to photography so the visual results will be performed by some other unbiased individuals. I would like to detail my experience with this side by side setup in a photographical sense. Please understand that both scopes are engineered very well and that I am a strong supporter of Sky Watcher due to their price point. That being said.......I am also a very honest person and nothing here has been fabricated as some may quickly assume. The AP160 scope is, without a doubt, an extremely nice scope to have.
I attended the Okie-Tex star party recently in Oklahoma and rented a private ranch about 2 miles from Camp Billy Joe. Okie-Tex skies are very nice and I had a nice opportunity to stretch the legs on both of these scopes photographically. The results may surprise you and they may not but I am here to detail what I personally found. First......here is the setup....
AP160: The AP is an F 7.5 scope with a monster Feather Touch focuser. The extra $1200 field flattener bumps this to F7.7. I also used a $135 DSLR adapter for the flattener. For this reason, it may appear just slightly dimmer in contrast than the SW picture.
SW150: Out of the box F7....no extra items needed. It comes with rings, a flattener and a t-ring for Canon cameras.
Cameras: I used two identical Canon 60Da cameras. All menu setting were matched and both cameras have a very low shutter count.
Capture: Backyard EOS Premium on one laptop.
Guiding: Orion SSAG using AstroTech AT65EDQ
Mount: A single Astro Physics 1200 was used with a dual saddle configuration. Guiding was real good as long as the wind was calm. Wind was my biggest battle in general. I took so many subs though that the bad ones were used in stacking and just got rejected.
Processing: I use PixInsight and the same basic workflow was used to process both pictures. The only real abnormal modification is that I scaled down the AP160 picture to match the SW150 picture exactly. PixInsight has a real nice tool for this. Both pics could then be processed side by side using the exact same techniques once cropped identically. 124 lights from each camera were used at 360 seconds each (6 minutes). 56 darks were collected and used on both rigs separately. I threw in 100 bias frames to scale the darks. No flats at all.
Target: NGC891 is an edge on galaxy in the constellation Andromeda. It is very similar in nature to NGC4565. You might ask why this target? Well, I chose this target as a runner for the comparison for several reasons. It's color is a bit deep and abnormal for most galaxies and it has a ton of dust that can be used for detail comparison. Just look at all the streaming dust in its lane! It also has a number of nice little galaxies in the background. Being as this was shot with a DSLR, I am very happy with the result and think it looks very good. I can only imagine what a nice CCD would have shown here. Stars in both scopes were pin point all the way out to the far corners on both sensors. So both flatteners did their job very well. The amount of chromatic abberation I am seeing around stars is no better or worse than what is seen in the other photo. This came as a surprise to me but you can see for yourself.
SW 150 PIC
AP 160 PIC
The only real differences I was able to distinguish is that the SW pic is slightly brighter (I am certain this is due to the slight difference in F ratio) and the stars are slightly cleaner around the edges on the AP picture. The CA seems to be about the same and I see no difference in detail whatsoever. Now....I know what you are thinking.....there is no way this is a good comparison! This is why all images were taken at exactly the same time (same sky quality) using the same mount and guiding (same error if any). The number of exposures are identical. I even went as far as to babysit the rig 100% because I dithered every 3 images. Therefore, I had to pause one of the sessions a few seconds while the other dithered the mount. The sensor from one camera sat and cooled NO longer than the other. I can thank Backyard EOS for the ease of use. Their software really helped in making this as simple as possible.
Bottom Line: Is one scope really better than the other? Only you can be the judge.