They can have what appears to be parallax. I think its caused by aberrations in the glass as they all claim to be parallax free. I had two with problems. At 25 yards I had 2 1/2 & 4" of movement. Both sent to the makers, they agreed and replaced the units. After searching the subject I ran into this exhaustive test of some average to very expensive dots. Some of the pricey models were way worse than the cheaper versions so testing is required if you need accuracy. Shooting large steel plates at short distance is probably not a downside unless the movement is terrible.

This is a long article so scroll to the bottom for the punchline or use patience. Posted this once before and some of the buyers of the expensive units came out of the woodwork to challenge the testing protocol as it did not fit their narrative. Read em and weep! Its a little older done in 2017.

Comparative Study of Red Dot Sight Parallax | Green Eye Tactical

 

Not all red dots are equal...just like regular scopes, some are better than others about how they handle parallax.

In rifle red dots, I believe EoTech is one of the best, some Aimpoints are good, some aren't, but I read a study where Leupold, Vortex and Trijicon were not all that great. Oh...I see jazzsax8 has it linked.

So you either spend the money and get a good one, or spend the money and get a bad one....or just get a good sight picture, and don't let it wander.

Personally, I see pistol red dots as a speed device, not an accuracy device. I'm sure one could shoot very accurately with them, but I think that takes the same skill set as irons, and provides no advantage, while the speed of target acquisition, transition and follow up shots is better with a dot....AFTER you train with them.

You want to hit lots of target A zones fast while on the move, get a red dot and practice. You want to shoot a bunny in the head...the red dot isn't all that helpful versus a good set of iron sights.

 

Shooting air guns at an even closer distance of 10m (33 feet), I learned long ago that red dots do very definitely have parallax and at that distance there is a huge range of how much parallax between all the models on the market. Some brands/models were totally useless when shooting for score or even casual plinking at that distance, but some were pretty good, though even the best had some parallax at only 10m. Take that marketing BS about being parallax free at all distances that some, but not all, red dot brands claim with a truckload of salt.

Probably not a coincidence that one of the better red dots I've used for close up shooting in terms of parallax are Ultradots and Ultradot actually advertises their dots as being parallax free at the specific distance of 50m (55 yards), not parallax free at all distances, so, yes, at 10m there is still some dot movement with the UDs.

In my experience, the Burris Fastfire III is also pretty good and that jives with the results of that listed study.

When accuracy testing with my air guns, though, I go right to a scope with an AO that can be adjusted for the distances I shoot, not a red dot. The red dot, though is a fun choice for shooting steel.

 

Thanks to all for their input on this red dot parallax issue. That is one heck of an article that jazzsax8 linked. While the article had a tremendous amount of data, my eyes started to bleed before I could finish reading it. Back to that Konus in my OP, I was really shocked at the amount of parallax I could plainly see... It was several INCHES at 50ft! I realize this may not be that serious of a problem, as your eye will naturally "center" the dot in the tube and limit the amount of parallax error. BUT, suffice to say I'm very happy that my Millett SP-1 has virtually NO parallax that I can see on target, using the same technique as with the Konus in my OP. The only thing I can think of is my Millett SP-1 red dot is older (guessing 10-15yrs) and is Japanese made, NOT ChiCom, so perhaps the lens quality is better in the Millett sight? Dunno, but I told my shooting friend I would NOT leave that particular sight on his pistol. To be fair, perhaps that Konus was a lemon, but it was the only example of that model red/green combo sight I have had a chance to look through. On a more humorous note, after he and I had a discussion about it, I jokingly said I should have kept this bit of info about his sight (the parallax issue) to myself, as we regularly compete against each other.

 

Can't give you a number, but no, it is not in inches

There is enough at 10m for me to not choose the UD when shooting for score, though, given how small those 8,9, 10x rings are. Still, I have managed some decent scores using a good red dot by carefully positioning my head on the stock consistently the same for every shot. That's a technique that will allow you to use a red dot when there is a parallax issue, but you need to be rigorous about getting your head/eye in exactly the same position, shot after shot. For me, it's just simpler/easier to use a scope with an AO that focuses down to 10m or even just use a good peep and globe setup.

 

Once upon a time, I read a post where using the UltraDot, they put something like heavy paper/cardboard in the front ocular with a hole in it that reduced the ability to get your view off center. Probably kind of like using a peep sight on a rifle. I am using the 30mm Matchdot II with 6 reticles but I think the one most used by the Bullseye crowd is the 1" model. Shooting it today so will check for parallax at the 25yds and closer ranges.

My Burris FFIII is excellent at 25 yards, not sure about closer ranges. It does seem to have a little aberration in the glass as my eyesight deteriorates the longer I use it.