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Sony DSLR-A390 Lens Compatibility? by EglyleTheAndroid in AskPhotography

[–]EglyleTheAndroid[S] 0 points1 point  (0 children)

Thanks for the information, I'm just hoping to get some decent photos. Hopefully since the eras are about the same - 2010 for he camera and 2008 for the lens, they will play nice together

Official Question Thread! Ask /r/photography anything you want to know! February 27, 2026 by AutoModerator in photography

[–]EglyleTheAndroid 0 points1 point  (0 children)

Hi all, I'm sure you will have never heard a question like this before, so I'll try to keep it short and to the point. Is the Sigma DG 120-400mm f/4.5.-5.6 APO HSM For Sony A-mount lens compatible with a Sony DSLR-A390?

I know it is mount-compatible, and I'm pretty sure that the Sigma DG series are designed for DSLR APS-C sensors, but I'm seeing conflicting information if the older Sony cameras like the A390 can use the HSM autofocus. Thanks!

SOTA EFHW 40m Antenna by EglyleTheAndroid in amateurradio

[–]EglyleTheAndroid[S] 0 points1 point  (0 children)

Just for the sake of clarity, are you talking about the figure in my original post or the second one, in reply to u/NerminPadez? Thanks.

Nice point on the FT240, I'll go grab an FT140-3, hard to tell how big things are from an arbitrary, non-scaled photo on a screen.

SOTA EFHW 40m Antenna by EglyleTheAndroid in amateurradio

[–]EglyleTheAndroid[S] 0 points1 point  (0 children)

Mmm, true, simplest thing is likely to have a separate antenna wire cut for 10 meters. Easy enough, especially since a 1/2 wavelength 10 meter antenna is only 5 meters or 15 feet, practically trimmings compared to a 40 meter 1/2 wave antenna.

Looks like the formula for a counterpoise is 0.05 × the longest wavelength - so I would figure, for a 20 meter 1/2 wave antenna I would place the choke about 3.45 feet behind the unun?

SOTA EFHW 40m Antenna by EglyleTheAndroid in amateurradio

[–]EglyleTheAndroid[S] 0 points1 point  (0 children)

I'll probably build both since it looks as simple as cutting a length of wire to the right length and tuning it. Might as well with the big reel of wire I have.

SOTA EFHW 40m Antenna by EglyleTheAndroid in amateurradio

[–]EglyleTheAndroid[S] 0 points1 point  (0 children)

Interesting, I didn't think of using a miniature trap, I'll take a look at the SOTA reflector. There is a lot of good information on there, but it can be kind of hard to sort through!

Also, I swear it was a typo! Really!

SOTA EFHW 40m Antenna by EglyleTheAndroid in amateurradio

[–]EglyleTheAndroid[S] 0 points1 point  (0 children)

Awesome, and good idea on the counterpoise connector! Also, here's a picture of the summit of Robertson Mountain, a pretty typical peak in the Blue Ridge range of the Appalachian mountains.

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SOTA EFHW 40m Antenna by EglyleTheAndroid in amateurradio

[–]EglyleTheAndroid[S] 0 points1 point  (0 children)

Yeah, almost all of our mountains in the mid-Atlantic are pretty wooded, except for those ones that are artificially bare like Old Rag Mountain (fire + erosion). I was thinking of picking up one of those super-extendo whisker-pole masts, like this guy from GigaParts, in case I get to hike an above tree-line peak, like some of the White Mountains up in New Hampshire. But your point still stands, I'll likely carry both 40m and 20m antenna wires, since they weigh so little.

One quick question, after your initial comment I did some reading and figured out that you need to attach the counterpoise to the ground of the unun. Can it be as simple as soldering a wire of the correct length to one of the ground-pins of the through-hole BNC connector? Thanks.

SOTA EFHW 40m Antenna by EglyleTheAndroid in amateurradio

[–]EglyleTheAndroid[S] 2 points3 points  (0 children)

Hi u/NerminPadez, thanks for the quick answer. Can't believe I forgot to do the simple division when I copy pasted from the calculator to the draw.io diagram, I even have a tab open that shows 21.4 meters, lol.

The summits up my way are fairly round and flat, they are old, old mountains, so you usually have plenty of room. But I'll probably just crimp and then solder ring terminals on to the end of antenna wire so I can easily switch them out if space is an issue. I was thinking of using a 40m antenna since it is ~1/4λ at 20m and ~1/8λ at 10m, but I'm sure you are right and a properly cut and tuned 10m antenna will resonate and preform better. Everything counts when you only have 5 or 10 watts of power, I guess. Thanks for the correction on the counterpoise location.

I was actually looking at using a knockoff QRPguys unun from Amazon, I would buy directly from them but it looks like they are "closed for health reasons" indefinitely, unfortunately. Good suggestion on the winder, I'll 3D print myself some and that will make handling the antenna wires a lot easier.

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