from APM140 SD F7 to FC100DZ ?

[Fedele]

Hi

Has anyone of you ever had the experience of switching from an APM 140 SD f7 (or similar) to an FC100DZ (or FS102 and similar)?
Can it be considered a complete defeat or a gain in "health"?

[F15Rules]

That's a BIG drop in aperture on a refractor...are you unhappy with the APM 140mm?

I've not used one, but I do have a Tak FS128 and I wouldn't want to swap down personally. No disrespect to the FC100DZ ( I know MikeDnight loves his). Mike has also owned an FS128, so he's better qualified than me to comment, but having owned two excellent Vixen ED103s scopes, they couldn't match the FS128 on light grasp and resolution.

I could understand a switch purely on portability grounds, but not optically🤔?

Dave

Edited June 2, 2021 by F15Rules
Typo

[Stu]

I agree with Dave. A lot depends on what you are trying to achieve. If you want much better portability and use ability, smaller mount requirement then yes, it makes sense. The views would be purer, with no visual CA and you may prefer then aesthetically but from a resolution perspective the 140mm would win the day. There are times when a smaller scope will best a larger one in poorer seeing so there are no absolutes really, but I think you need to clarify what you are trying to achieve first, before you can get more informative answers.

[John]

I have a 130mm F/9.2 LZOS triplet refractor and a Tak FC100-DL and the difference in performance between the two is quite obvious. Both excellent but 30mm more excellence certainly shows itself.

The ease of setup and use is also very different though with the 100mm refractor being much more of a "grab and go" affair. I need to plan sessions with the 130mm F/9.2 somewhat more.

I can imagine circumstances where a person might make the step from a 140mm refractor to a 100mm but the motives there would be more about ease of use, portability, lighter mounting requirements etc. If the step was to something like the Tak TSA120 then the performance reduction might not be as marked and maybe marginal on many targets.

 

[Fedele]

 

let's see if you share my thoughts.

On the one hand I have the choice of the APM 140 SD f7. A lot of diameter but a lot of space.
Taking it I would see much more on the deepsky, much more on the moon, I would have a lot of resolution also on the sun and I don't know what visual rendering on the planets (on this I ask you). On the other hand, I would have a perspective to use only at home, which I could not carry around (even if I am sedentary, I only move from home in the summer when I reach my place of holidays by the sea).
Notwithstanding that I have to equip myself with a 25/28 cm mirror for planetary imaging with webcam (c9, C11, etc), a 140 and the APM 140, I don't think it could ever excel with a C11 on the DSO view.
Another hypothesis is that I also equip myself with a large diameter Dobsonian for the DSO soplo.
At this point I see the APM 140 option as the prevailing telescope in the balance.
the alternative would be a FC100DZ.
This telescope would be light, portable, I would use it a lot more, etc ...
Of course there is no comparison between the two diameters, but I think that for large star fields at medium magnification or on deepsky objects, I could use a cheaper achromatic refractor: 150/1200 or better still a 150/750.
I would thus have the excellent small telescope of excellent quality and transportable which would allow me to save on the purchase of other small telescopes to transport, and in that case I would have the large diameter refractor for starfields and wide DSOs (even on the sun).
this option would allow me to invest in other materials as well.

I'm uncertain.

Better to focus on the large diameter and APM quality factotum or the second option?

thank you

 

Edited June 2, 2021 by Fedele

[John]

I'm sure this is very interesting but the black on dark grey text is very hard to make out. Could you change that colour scheme ?

 

[Fedele]

Sorry  for english

Later i will edit

[Deadlake]

I believe the 140 mm has got a poly-Strehl around 0.92, so how many nights of the year will you be able to make use of a scope with a higher Strehl? 

Note, TMB defined 0.95 Strehl as a limit where a scope would be seeing limited most nights of the year, so why engineer more?

I’m sure your SXD2 would be able to handle the 140 mm, so unless portability is a requirement I’d go with the larger aperture.

Also how much overlap with you Mewlon 180?

Always good to have a 4” for flexibility, does it need to be a DZ?

Edited June 2, 2021 by Deadlake

[BGazing]

If you own neither...start with  a 100 mm refractor. Sweet spot.

140mm is a lot to handle. You need to see it in person in order to decide if you want to lug it and it needs a completely different class of mount.

[John]

12 minutes ago, Fedele said:

Sorry  for english

Later i will edit

Nothing wrong with the english at all - it was only the colour that I found hard to see

Nice and clear now !

 

Edited June 2, 2021 by John

[Stu]

26 minutes ago, Fedele said:

I would thus have the excellent small telescope of excellent quality and transportable which would allow me to save on the purchase of other small telescopes to transport, and in that case I would have the large diameter refractor for starfields and wide DSOs (even on the sun).

Given that portability and use ability seem strong factors, plus I think you are saying you have, or would have a larger aperture newt available, the DZ sounds like a choice worth considering.

[JeremyS]

If portability is paramount, the FC 100 DZ will give you great satisfaction.

If you still wanted a bit more aperture and happy to move something a bit bigger, then there is the TSA 120.

[Deadlake]

How much wide field viewing would you imagine doing with the scope, e.g. with an Ethos 21 mm or APM 20 XWA? My SD103S does not have enough infocus for either of these EP’s so I need to use another scope and I suspect the 100DZ has the same limitation. The APM 140 will not had the focuser has the range to accommodate these EP’s.

[jetstream]

23 hours ago, Fedele said:

Another hypothesis is that I also equip myself with a large diameter Dobsonian for the DSO soplo.

Everyone should have a large aperture dob IMHO, if circumstances allow. A 1/10 wave mirror, .98 Strehl is not needed- just a nice smooth 1/4 wave system is all thats needed. They really do show more of DSO than other scopes, under dark skies espc.

[Deadlake]

11 hours ago, jetstream said:

Everyone should have a large aperture dob IMHO, if circumstances allow. A 1/10 wave mirror, .98 Strehl is not needed- just a nice smooth 1/4 wave system is all thats needed. They really do show more of DSO than other scopes, under dark skies espc.

With your dark skies @jetstream you can see quite a lot due to the contrast you have.  Even with your TSA-120. However with portability in mind to get to a dark sky a smaller scope might be the answer. I’d imagine a Mewlon 180 would be very good  which @Fedele already has. Presume that’s not portable enough???

[Gonariu]

On 2/6/2021 at 22:16, Fedele said:

Ovviamente non c'è paragone tra i due diametri, ma penso che per grandi campi stellari a medio ingrandimento o su oggetti del cielo profondo, potrei usare un rifrattore acromatico più economico: 150/1200 o meglio ancora un 150/750.

I was advised against the achromatic refractor 150/1200 (I was eyeing the Bresser) because it is too heavy, it seems that even an EQ6 is inadequate to support it. The 150/750 refractor is certainly more manageable, on the deep sky it must be very beautiful, on the Moon and planets there are those who argue that a good filter is enough to reduce chromatism but I think many disagree. Clear skies and no wind at all (here in Sardinia the mistral is very disturbing ... .....) !!!

[jetstream]

6 hours ago, Deadlake said:

With your dark skies @jetstream you can see quite a lot due to the contrast you have.  Even with your TSA-120. However with portability in mind to get to a dark sky a smaller scope might be the answer. I’d imagine a Mewlon 180 would be very good  which @Fedele already has. Presume that’s not portable enough???

A Mew 180 would be great for galaxies but the limited TFOV will hinder some nebula and starfields etc. Actually Im not sure if the Mew 180 is that limited- I wonder if the scope acts as a "field stop" before 46mm is reached with an eyepiece? ie will it vignette with a 42mm LVW class eyepiece?

[Fedele]

Yes i have the Mewlon and a 120ED SW (first serie). Its contrast make good also the M42 view. Contrast and high precision of optics play an important rule. 

i m buying: 

- a Mak 127 for Moon e planet imaging in holidays (no...the baby Mu can't)

- TS refractor Ed FPL3 80 F7 to use it with Daystar Combi Cromo for full disk. I think this will be the grab and go rich field telescopoe. i don t know how indicate is for this work the 80 mm. Other question.... it can rwch focus with a Maxbright II?

- i thinking to the Acro 120/600 or best the 150/750 acro, for reach fields primarly, moon at low x, sun.  What is  the more light 150/750 do you know? for Bino i will cut the tube!!

Alternative to all this: 

FC100 DZ

it is hard and i m evaluate if FC100DZ can really do all this. 

Edited June 4, 2021 by Fedele

[Gonariu]

Having already got a 120 ED which I guess has the 900mm focal length, surely a 127mm Maksutov for the ultra-portable planets for the holidays must be very nice; I am intrigued by the mak 90/1250 for its yield and compactness, it is certainly better than my 120/1000 (Konusuper 120) diaphragm at 90 mm because the achromatic doublet is chipped laterally. I don't know for 150/750; surely it is a nice telescope for the deep sky, for the Moon and planets there are those who see it badly and there are those who say that with a special filter the problem of chromatism is solved well, perhaps it depends how and how much the spherical aberration, far worse than chromatic aberration. I have a Ziel 120/600 refractor that I used on Mars at 200X on the last opposition giving good results for a short focus achromatic, on deep sky I used it much less.